Archive for December, 2011

Snow showers east and north Monday night

December 31, 2011

1. A strong cold front will push through the region Overnight. With it a surge of Warm air advection will occur causing temperatures to fall into the 38-45 range before rising a few degrees by sunrise. temperatures will fall back into the upper 30’s to mid 40’s by Sunday afternoon with winds from 15-30 mph with gusts to 35-40 mph. A wind advisory has been issued for most locations north of the southern ky pkwy. Also i can’t rule out a passing shower as well. Skies should be mostly cloudy.

2. Monday the flow turns northwesterly behind the front with winds from 20-25 mph and higher gusts. Highs will range from the low to mid 30’s after lows the upper 20’s and low 30’s. The northwesterly flow will promote the transport of some lake moisture into the region and with the high terrain in southeast KY some light snow showers could occur called upslope by Monday night. A vort max coming through will enhance the activity a little bit promoting flurries for northern/eastern KY and the Lexington region as well. I’m only expecting very light amounts of QPF with a warm ground. Any accumulation of a few tenths of an inch of snow from any snow showers will be patchy. Perhaps the highest elevations along the VA line see an inch. This is by no means an attack of snow squalls. Still only a 30% chance this gives Lexington the first measurable snow of the season.

3. Will not make a snow map due to the scattered and light nature of this snow chance. Lows Monday night will fall into the teens for many with some low 20’s in the south leading to a concern for slick spots with any light snow showers.

4. Tuesday will be a struggle to 30 for many for highs. Clouds should clear out as the disturbance moves to the east of our region winds will become lighter as well.

5. Feeling confident about Jan Forecast made earlier this week for above normal temps after seeing the false MJO signal of a favorable phase for cold go away and the PNA go negative. not good for snow and promotes lakes cutters. I’ll fix the maps in the last post that were not working right.

Advertisements

Jan forecast: past winters package reduced, remaining years still match euro weekly forecast

December 29, 2011

Winter forecast temps ( from a few months ago)

With December in the books some edits will need to be made to the original forecast. It has been much warmer in the east, Great Lakes and Ohio Valley likely due to the cold PDO. This has also allowed a deeper trough over the southwest which led a white christmas in northern Mexico. Most of the analogs did not have the extreme effects of a cold PDO but were in cold PDO periods where it did not have as much effect. So far of the original analog package has been reduced. The winters of 56-57 and 71-72 best match December conditions so far.

Within the original analog package was the threat for cold either in December or January.  Now some of the years left in the analog package Overall I feel January will average out slightly above normal temperature wise. stratospheric warming will play in role in disrupting the positive nature of the AO. The strong positive AO has also been something the original winter forecast did not account for. The most interesting point of this revision is the cold February featured in the 71-72 year.

The euro weekly product resembles the 71-72 analog for january while the CFS has a blowtorch.

The euro however is slightly warmer in the southwest. It should be noted the euro did not have the southwest chill or this cold shot to start 2012. 1957 looks similar to this but cooler over the great lakes and northeast. The long range euro supports this to some degree.

Let’s take a look at the stratosphere once again

Current

Day 5

day 10

Several stratospheric warming episodes are expected over the next 10 days. These usually have a 2-3 week lag time and should cause the strong positive AO to be broken some. very cold air is locked in over Canada to get a push of that extreme cold into the US the colder region with the L known as the Polar vortex PV would have to weaken quite a bit more or push to our side of the globe.  This could happen by February.

looking ahead there is some hope for colder times with snow threats in the later half of winter. The CFS does indicate some arctic air should enter the northern plains also take a look what 71-72 featured temperature wise for February.

However it should be pointed out that most late winter and early spring periods during a la-nina are very mild for our region. We’ll see.

Updated forecast for Jan temps

Forecast for rest of week

December 28, 2011

To recap Tuesday:

– the low cut further northwest but just slightly this allowed a wedge of WAA for a few hours to be located farther west over BG/LEX thus the temperature rose to 46 instead of the low 40’s. This made all the difference on the back edge of the precipitation instead of mid 30’s has upper 30’s. Also rain was underdone for Bluegrass.

– Could have been more bullish on snow shower chances behind main system as well.

Forecast:

Highlights

– Week clipper systems passing to our north 

– Overall still very mild

– Several windy days as well 

Forecast: 

-A week clipper system will track across the great lakes Thursday, with it a warmer airmass will move into the region along with a mix of sun and clouds. High temperatures Thursday after a chilly start should rise to 53-58 in the south with highs around 50 north. A stray sprinkle or light shower cannot be ruled out either for the south with a decent shot at scattered rain showers for northern regions.

Another week clipper system will move through the great lakes region once again on Friday bringing with it another surge of warm air. Lows will be in the 40-45 range  south and in the upper 30’s north. Highs should get around 60 in the south Friday with 50’s elsewhere. This is several degrees above model guidance but usually model guidance is usually to cool in these set-ups. A concern would be if the clipper track was farther south which would increase the chances for passing rain showers and lower high temperatures Friday. Current thinking however only has a passing shower Friday, similar to Thursday with a track farther to the north. On both days winds will be gusty as well from 13-19 mph with gusts to 30 mph at times.

3. On Saturday once again we’ll have a mix of sun and clouds with highs from 52-57 south a few degrees cooler northern regions after starting out in the 35-40 range regionwide, winds will be lighter. For New Years day a strong frontal boundary is likely to move through the region. Timing of this boundary is still not entirely certain at this time which will have a large impact on temperatures. Right now the front should pass through the region in the afternoon. So this means clouds and warm air advection should increase with a chance for rain showers ahead of the front. Overnight temperatures New Years Eve should stay in the 40’s with highs reaching the upper 40’s to low 50’s Sunday before falling rapidly by late afternoon.

4. This leads to a likely cold start for the New Year however now no signs of the first measurable snow of the winter season are in the forecast. The pattern does not appear favorable anytime soon as we approach the halfway mark of meteorological winter. The winter of 1931-32 was snowless with several others having a trace for the entire winter. As it stands now a trace has fallen this season which would be the second least snowiest winter on record, quite a reversal from last year. 

Discussion:

– I’ve gotten burned with temperatures on the warm end of clippers many times in the past. It will be warmer than guidance. Unless the euro track is correct this would provide more clouds and rain. Models have a poor handle of advection.  

– Temperature spread was large within the guidance generally went warm with the clippers and ahead of Sunday’s front.

– Good agreement on gusty winds over the next several days except Saturday.

– I’ll update Sunday’s front more later this week along with a January forecast.

rain changing to snow Tuesday?

December 26, 2011

A low pressure system will move into the Tennessee valley tonight and Tuesday before moving into the mid-atlantic states. In the warm conveyor belt plenty of moisture will be drawn north in addition to a decent amount of isentropic lift. Periods of rain should develop for tonight and Tuesday morning. The region will be dry slotted for a time Tuesday before a secondary period of precipitation moves through on the backside. Temperatures overnight should be steady from the upper 30’s to low 40’s.

With the last system you recall the rainfall forecast was slightly overdone. This was due to thunderstorms over the south robbing the region of moisture coming our way. Once again mixing ratios are around 5 g/kg in the south with mixing ratios around 3 g/kg in the north which would indicate around an inch of rain in the south with half an inch in the north. Once again convection to our southeast which shows well on SPC WRF could keep rainfall amounts slightly lower than that from 1/4-3/4 inch, though the SPC WRF shows more rain, modeling always shows too much precipitation. Experience says go lower!

Around 12z Wednesday modeling is indicating a secondary region of 700 mb  enhanced Omega over Western Kentucky coupled with forcing/lift due to the temperature contrast known as frontogensis. This should get banded or a band of precipitation on the backside of the system. This area of precipitation should track northeast into northern Kentucky through the afternoon. This region should get into Bowling green and Lexington for a time.

The cooling processes mentioned for the banded backside precipitation is known as dynamical cooling where precipitation falls to cool the atmosphere. Right now I think this should occur allowing the temperatures to fall into the mid 30’s during the time while the secondary precipitation region is moving through. I think it is questionable as if Lexington and Bowling Green see a changeover but points to the northwest should see an hour or two of snowfall with up to 1/2 inch accumulation. A few spots may even see slightly more with heavier snow rates say along I-71 or in the Elizabethtown region.  After the precipitation ends however temperatures should rise a degree or two closer to 40 thus even if does snow during the small window any accumulation on a very warm ground will melt and roads will remain well above freezing and wet.

In terms of guidance agreed with elements of the SPC-WRF though a few hrs slow, the 12z NAM/ECMWF runs as well looked good. GFS had a poor time capturing the mesoscale features as was not used. Overall went with raw NAM/ECMWF guidance on temperatures and went a little higher than all guidance for winds Tuesday around 13-19 mph with gusts to 25 mph.

– winds become lighter and skies clear for Wednesday as high pressure builds back in. Highs will range from the upper 30’s north to mid 40’s south. Lows will be in the mid to upper 20’s Wednesday morning.

As promised first snow map of the season!

zone 1- rain changes to snow from late Tuesday morning through the mid-afternoon. A few hours of steady snow which accumulates up to 1/2 inch on grass locally higher amounts. timing from west to east.

zone 2- 50% chance rain changes to steady snow for an hour or two early Tuesday afternoon and mid afternoon bluegrass. evening flurries. under 1/2 inch of snow on grass.

zone 3- rain then evening flurries, highest elevations may see a steadier snow with coatings up to 1/2 inch late in the afternoon or evening. concerned temps may rise in the AM into the mid 40’s southeast.

Long range: Euro weekly model appears to be wrong for next week. Modeling operational ECMWF, CMC and JMA  show a deep trough over the region for the middle part of next week this would not equal warmer than normal weather and in fact could bring more chill  and snow chances.  If you follow the 4th most accurate model the GFS it will come around to that hopefully sooner than later.

update coming

December 26, 2011

will update after 12z ECMWF with the first snow map of the year! Looks like rain tonight and Tuesday morning changing to snow in BG/lou around 17-18z for an hour or two. Lex/Cvg should see an hour or two of snow around 21z.  Overall accums should be under 1/2 inch if any. eastern KY will see rain end as snow showers and flurries with little or no accumulations.