Cold Air on the Move; Strong Storms Possible Later Today...

As advertised, arctic air is on the move across the central and northern Plains this morning, and I think you can pick out the cold front on the latest surface temperature map above!



If you're a true fan of the weather, you've got to love the contrast across that front!  Temperatures in the lower to middle 70s in central Texas right now, and in the teens below zero in North Dakota!



The front is forecast to advance rapidly Southward today, reaching a line from southwest Texas through the middle Mississippi Valley by late this afternoon or early this evening.



Strong to locally severe thunderstorms are possible ahead of the front, as indicated on the latest forecast from the Storm Prediction Center (SPC) in Norman, OK:

The greatest chance of storms producing hail and/or wind gusts to severe limits will be within the yellow shaded area on the image.  A lesser risk exists within the brown shaded areas.

An isolated tornado also cannot be ruled out, especially within the brown shaded area on the image below, extending from the ArkLaTex region across central and eastern Arkansas:

The main threat of strong to severe storms ahead of the front will come from mid to late afternoon into this evening.  If you live in the severe weather threat areas, please remain alert and listen to NOAA Weather Radio, local media or another trusted source for the latest information and possible warnings.

As I've been saying for several days now, the drastic change in temperature will be one of the most noticeable affects of this system.  Note the dramatic difference between the forecast high temperatures today:

...compared to mid-afternoon readings tomorrow:

An unusually long duration and early freeze will take place across portions of southcentral and southeastern Texas on Monday night and early Tuesday, including the Austin-San Antonio area.  The potential exists for 11-12 hours of sub-freezing temperatures (from roughly 9pm Monday through 10am Tuesday), along with 7-8 hours with readings in the middle 20s during the pre-dawn hours of Tuesday morning.  This is very unusual for so early in the season across this region, and folks should take appropriate measures today to protect and/or bring in tender outdoor vegetation.

Here's a look at the forecast minimum temperatures across the southcentral U.S. for Tuesday morning:

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First of Several December Winter Blasts on the Way...

Cold air is gathering across the northcentral U.S. this morning, and is destined to make a major move to the South on Sunday and Monday, spreading the coldest air so far this season into much of the southcentral U.S.

The cold front is forecast to stretch from southwest Texas into the Midwest by tomorrow afternoon at 3pm.  You can pick out the front nicely on the NAM computer model forecast temperature image below, valid at 3pm CST on Sunday:

At least a broken line of thunderstorm activity likely to form along and ahead of the front, and some of the storms may become strong to severe across the South.  The forecast radar image below is from the high resolution NAM model, valid at 9pm CST on Sunday evening:

As I always caution when examining a model depiction of the radar at a future date/time, use caution.  While it is not likely that thunderstorms will exist exactly where shown, you at least have a good idea as to where the best chance of storms will be.

There is a chance for some of the stronger storms to produce hail and/or wind gusts to severe limits, and the Storm Prediction center is forecasting that risk within the brown and especially the yellow shaded areas on the image below for tomorrow afternoon and evening:

For folks across the South, the major news with this system will  be the sharply colder temperatures.  For example, the Austin/San Antonio area in Texas will plummet from readings in the lower 80s on Sunday afternoon: 

...to readings in the 40s on much of the day Monday:

Strong Northerly winds of 20-30 mph with gusts to 40 mph are likely behind the front on Sunday night and Monday morning, which will drive wind chill values into the 20s and 30s across a large part of the southcentral U.S.  The image below depicts forecast wind speeds near the surface at 6am CST on Monday morning.  Gusts of 30-40 mph are likely within the green shaded areas:

At this time it appears that wintry precipitation will be relatively scarce in association with this first major system of December, as far as the central and southern U.S. is concerned.  The high resolution NAM computer model suggests that some accumulating sleet and/or snow may take place in a relatively narrow corridor from the Texas panhandle into southwestern Oklahoma on Sunday night and early Monday.  The image below is valid 6am CST on Monday:

We'll need to watch this general area closely for any significant changes in how the system comes out with respect to precipitation potential behind the cold front Sunday night and early Monday.

A widespread, hard (killing) freeze can be expected across much of southcentral and southeastern Texas (areas that have not had one yet this season) on Monday night and Tuesday morning.  In the Austin/San Antonio area for example, the potential exists for sub-freezing temperatures for a period of 8-10 hours - including a 5-6 hour period with readings in the middle to upper 20s.  This is very unusual for so early in the season in this area.

As I've been talking about for a week to 10 days now, this cold blast will be just the first installment in what looks to be a much more active December weather pattern with respect to cold weather, as well as wintry precipitation in some areas...so stay tuned!

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Colder / Snowier Outlook Still on Track...

In a post last Friday, I remarked that winter weather lovers should take heart as a major change in the weather pattern would get underway later this month, bringing an end to unseasonably warm weather across much of the nation.  



I've continued to monitor the situation since the post was initially made, and I'm happy to report that the forecast is still on track... which is great news for those of us who are sick and tired of 70 and 80 degree weather in late November and early December.



To set the stage, brutally cold weather continues in Alaska and Canada, where temperatures are in the 30s, 40s and even 50s below zero (degrees F) have been observed for the last several days:

The -36 degree weather in Fairbanks on Monday wasn't cold enough to keep some college students from throwing a beach party:

...which gives new meaning to the word frostbite (please don't try this at home, folks).  

The atmosphere likes to balance itself out.  When it's really cold in one area, it generally tends to be really warm in another.  The "other" place recently has been much of the lower 48 U.S., where temperatures continue to average above normal.  

The image below shows the departure from normal temperatures for the period today through the 10th, showing the bullseye of "above normal" conditions shifting into the southeastern U.S. during the period:

All of that cold air up in Canada and Alaska is very heavy and dense, and will begin to force its way Southeastward into the lower 48 U.S. from mid through late December, as shown on the same departure from normal computer model forecasts below, valid for days 5-10 (December 10th-15th):

...and continuing through days 10-15 (December 15th-20th):

By the day 10-15 period (December 15th-20th), you've no doubt taken note of the brutally cold air (as noted by the purple departure from normal values) shifting South from Canada into the lower 48 U.S.  That is a trend that I believe will continue through late December and into January.

Increasing jet stream energy in the middle and upper levels of the atmosphere will also come into play during the month, which will develop and increase a large snow pack across much of the central and northern two-thirds of the nation.

One such disturbance will produce a band of locally heavy snow from southwest Kansas across southeast Iowa and the upper Midwest late this weekend and early next week:

This trend is forecast to continue into the middle and latter part of the month, as indicated by the longer range computer model depictions below.  I wouldn't necessarily pay attention to the amount of snow shown on these longer range images, but they should give you a good idea as to the general areas that are most likely to be impacted.

The first set covers the period December 15-20:

...and the second set leads us from December 20 through Christmas Day:

Each panel within the image shows the "opinion" of the 4 different computer model simulations that were generated for the given period.

The snow pack will not only serve to deliver that "winter feel" to a large part of the nation later this month, but will also tend to preserve cold air intrusions from the North.  As the cold air moves South, it tends to moderate as it encounters warmer ground and air temperatures.  With a heavy snow pack in place, the ground and air will be cooler, thereby reducing the amount of warming that takes place as the airmass moves Southward.  This should generally lead to gradually colder airmasses remaining "intact" as they move further south across the nation.

So, there you have it.  I am still confident that the middle and latter half of December, and likely into January, will be much more representative of winter than what we've seen so far.  Keep in mind, winter doesn't even "officially" begin until December 21, so we still have a long way to go here!

On the other side of the coin, folks in drought stricken portions of the South and into the Mississippi and Ohio Valley region are ready-set-go for any type of moisture that will come there way, regardless of its form (rain, sleet, ice or snow).  While cold air intrusions by themselves don't guarantee an increase in moisture, there are signs that a more active jet stream pattern will gradually increase the chance of measurable precipitation across the region.

The following images show cumulative precipitation totals from the GFS and the European computer forecast models, respectively.  They are valid for the period today through Thursday, December 13th:

While the forecast model's don't provide a specific precipitation accumulation forecast beyond the time ranges above, in general, they continue to suggest that an increasingly unsettled pattern will develop across portions of the southwest and southcentral U.S., which would generally equate to greater chances of precipitation across portions of Texas and Oklahoma.  

The general position of the jet stream is noted by the green arrow on the image below, and I've circled in yellow an area of increasingly unstable conditions that should translate into the southcentral U.S. during the week leading up to Christmas.  This would generally lead to an increased chance of rain and/or snow across this region.  The image itself is valid at 6am CST on December 21st:

For those who are interested, the brighter red shaded area extending across portions of the Pacific to Alaska indicates a "ridge" of high pressure pushing into the region, which should cause the jet stream to "buckle" and send additional shots of cold air Southeastward toward the continental U.S.  I've attempted to illustrate this on the identical image below:

The bottom line on all of the above is that a much more active weather pattern is instore for the lower 48 U.S. from next week, into the foreseeable future.  Stay tuned for details as this situation unfolds...

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NWS/NHC "Modifies" Hurricane Warning Requirements in Wake of Sandy...

A spokesman for the National Weather Service's (NWS) National Hurricane Center (NHC) announced today that the requirements for the issuance of a Hurricane Warning will be modified effective next season.  



According to Chris Landsea of the NHC, the definition of a Hurricane Warning will be revised to read as follows:



An announcement that sustained winds of 74 mph or higher are expected somewhere within the specified area in association with a tropical, sub-tropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds. The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less than hurricane force.



Note that the system in question may now be "sub-tropical or post-tropical" and still qualify for a Hurricane Warning.  You probably recall that the NWS/NHC had forecast Sandy to become a non-tropical system before making landfall, which is the reasoning they cited behind the decision not to issue hurricane warnings ahead of that devastating system.



In the opinion of myself and many others in the meteorological community, Sandy was still a tropical system, and specifically a hurricane, at landfall, but that is neither here nor there for purposes of this particular article.



Landsea went on to say that "Sandy was not ideal, and the way we handled it was not right.  But we're fixing it."

It is highly unusual for the NWS to make such a move so quickly following an event.  I firmly believe this action is a sign of two things:  (1). an immediate response to the heat that they've been under for the last few weeks regarding some aspects of how the situation with Sandy was handled and (2). a fear of what may be revealed and/or presented during the upcoming review by an internal assessment team charged with making "recommendations" as to how better handle such a situation in the future.



Much controversy still surrounds the formation and execution of the assessment team, especially with regard to whether or not the government can be expected to be "independent and objective" when reviewing itself.  I steadfastly maintain that a fair, objective, independent review will not be able to take place as long as the government is in charge of "assessing" itself.



Today's announcement by Landsea was made at the headquarters of AccuWeather, a Vice President of which (Mike Smith) was to have co-chaired the original Hurricane Sandy Assessment Team.



Putting all of the various Sandy controversies aside, this is generally a good move that will allow the appropriate warnings to be issued in the future and should decrease confusion among the general public and those responsible for taking action to keep communities safe in this type of situation.  I still feel that storm surge needs to be addressed more clearly as well, and the NHC has promised that such a review is underway with a formal action plan to be detailed prior to next season.

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Say Cheese!

NOAA's GOES-East weather satellite had a surprise visitor on the visible channel yesterday afternoon:  the moon.  Say cheese!

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Oklahoma Was Balmy Again Today; Taste of Reality Likely Next Week...

Much of the Sooner State basked in upper 70 to lower 80 degree warmth today, a far cry from what you'd expect on the 3rd of December.

A cool front is passing from Northwest to Southeast across the state at this time, and will bring readings back down to earth a bit for tomorrow, but high temperatures will still be very pleasant, averaging in the 60s in most areas.

As pointed out in a post last Friday, major changes are in the offing for next week and beyond, as several shots of cold air at the surface and increased instability in the middle and upper atmosphere will combine to bring more seasonable conditions to the region.

The first storm system and cold shot is forecast to affect Oklahoma next Monday, or exactly 1 week from today.  Temperatures will average 10 to 20 degrees below normal across most of the state next Monday and Tuesday, with a pocket of values from 20 to 30 degrees below normal across the Northwest corner and the panhandle region:

Computer forecast models are also consistent in depicting a band of moderate to locally heavy snow in association with the cold frontal passage and middle level storm system.  The latest GFS computer model forecast valid 12 Midnight on Monday evening / early Tuesday morning of next week shows a band of locally heavy snow across portions of northcentral and northeastern Oklahoma:

We obviously have several days to pinpoint this situation, and some changes may take place.  The main emphasis for now should be that weather conditions will be much colder and somewhat wetter across the region in about a week, which will shock those who aren't expecting it (especially given the very warm conditions as of late).

The overall large scale weather pattern continues to suggest that this will only be the first of several shots of winter weather for the country for the middle and later portions of December, and likely continuing into January as well.

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Christmas Lights 2012

I was finally able to put the finishing touches on our outdoor Christmas lights this weekend:

This year it dawned on me that the "Merry Christmas" sign over the garage has been with us at 4 different homes over the last 12 years now.  They don't make light sets like that one anymore!  I've never had to replace a single bulb on that set in over 12 years, yet I've had to repair or replace most everything else numerous times!  What do you know - it was made in America...



In case you're interested, the actual lighting "ceremony" went something like this:

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