(12-11-10) Dry Slot Now Visible

As predicted by the models I discussed earlier, a nice dry slot is setting up behind the cold front. A dry slot is a pocket of relatively low moisture in the atmosphere caused by a low sucking in cold air from Canada. This can be seen clearly in the water vapor image below. I've placed a Low on the spot where the low currently sits. The white images you see are not clouds, but rather water vapor in the atmosphere. Water vapor in large quantitites is needed to form any significant weather system. The brighter the white, the more the vapor is present. You can see that this system is bright white along the cold front and the Low. But you can also see a darker swath of air coming into the center of the low pressure. This represents the absense of moisture.

Lows move in a counter-clockwise direction and essentially its sucking down cold, dry air from Canada into this low. This is partly why the cold front will be so impressive, bringing significantly colder temperatures to our area once it passes. This is the dry slot I've been talking about. This can also be seen by looking at the radar image below. Rain is only infront of the cold front and none behind.

What does this mean for us? It means that we shouldn't get much in the way of snow accumulation overnight once the front passes. I expect we will see some, but it won't be much and this will drastically cut down on our totals.

(12-11-10) Winter Weather Advisory Issued

As expected, the Louisville National Weather Service has issued a Winter Weather Advisory for Dubois County and all the Louisville NWS area. The Paducah office has chosen to issue just a statement rather than an advisory.

The text of Advisory in effect for Dubois County is below:

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE LOUISVILLE KY
301 PM EST SAT DEC 11 2010

...PERIODS OF SNOW AND BLOWING SNOW EXPECTED TONIGHT THROUGH
MONDAY MORNING...

.A STRONG COLD FRONT WILL MOVE THROUGH THE OHIO VALLEY OVERNIGHT
TONIGHT. TEMPERATURES BEHIND THE FRONT WILL FALL QUICKLY...CHANGING
THE RAIN OVER TO A WINTRY MIX AND FINALLY TO SNOW BY SUNDAY
MORNING. THERE WILL THEN BE A BRIEF BREAK IN PRECIPITATION BEFORE
MOISTURE FILTERS BACK IN FROM THE NORTH AND WEST. PERIODS OF SNOW
WILL BE POSSIBLE ACROSS THE REGION THROUGH MONDAY MORNING.
ADDITIONALLY...WINDS WILL PICK UP SUNDAY MORNING WITH GUSTY WINDS
CAUSING BLOWING SNOW WITH VISIBILITY REDUCTIONS.

INZ076>079-083-084-089>092-KYZ023>043-045>049-053>057-061>067-
070>078-081-082-121000-
/O.NEW.KLMK.WW.Y.0014.101212T0600Z-101213T1800Z/
ORANGE IN-WASHINGTON IN-SCOTT IN-JEFFERSON IN-DUBOIS IN-
CRAWFORD IN-PERRY IN-HARRISON IN-FLOYD IN-CLARK IN-HANCOCK KY-
BRECKINRIDGE KY-MEADE KY-OHIO KY-GRAYSON KY-HARDIN KY-BULLITT KY-
JEFFERSON KY-OLDHAM KY-TRIMBLE KY-HENRY KY-SHELBY KY-FRANKLIN KY-
SCOTT KY-HARRISON KY-SPENCER KY-ANDERSON KY-WOODFORD KY-
FAYETTE KY-BOURBON KY-NICHOLAS KY-NELSON KY-WASHINGTON KY-
MERCER KY-JESSAMINE KY-CLARK KY-LARUE KY-MARION KY-BOYLE KY-
GARRARD KY-MADISON KY-BUTLER KY-EDMONSON KY-HART KY-GREEN KY-
TAYLOR KY-CASEY KY-LINCOLN KY-LOGAN KY-WARREN KY-SIMPSON KY-
ALLEN KY-BARREN KY-MONROE KY-METCALFE KY-ADAIR KY-RUSSELL KY-
CUMBERLAND KY-CLINTON KY-
INCLUDING THE CITIES OF...PAOLI...SALEM...SCOTTSBURG...MADISON...
JASPER...MARENGO...TELL CITY...CORYDON...NEW ALBANY...
JEFFERSONVILLE...HAWESVILLE...HARDINSBURG...BRANDENBURG...
BEAVER DAM...LEITCHFIELD...ELIZABETHTOWN...FORT KNOX...
MOUNT WASHINGTON...SHEPHERDSVILLE...LOUISVILLE...LA GRANGE...
BEDFORD...NEW CASTLE...SHELBYVILLE...FRANKFORT...GEORGETOWN...
CYNTHIANA...TAYLORSVILLE...LAWRENCEBURG...VERSAILLES...
LEXINGTON...PARIS...CARLISLE...BARDSTOWN...SPRINGFIELD...
HARRODSBURG...NICHOLASVILLE...WINCHESTER...HODGENVILLE...
LEBANON...DANVILLE...LANCASTER...RICHMOND...MORGANTOWN...
BROWNSVILLE...MUNFORDVILLE...GREENSBURG...CAMPBELLSVILLE...
LIBERTY...STANFORD...RUSSELLVILLE...BOWLING GREEN...FRANKLIN...
SCOTTSVILLE...GLASGOW...TOMPKINSVILLE...EDMONTON...COLUMBIA...
JAMESTOWN...BURKESVILLE...ALBANY
301 PM EST SAT DEC 11 2010 /201 PM CST SAT DEC 11 2010/

...WINTER WEATHER ADVISORY IN EFFECT FROM 1 AM EST /MIDNIGHT CST/
SUNDAY TO 1 PM EST /NOON CST/ MONDAY...

THE NATIONAL WEATHER SERVICE IN LOUISVILLE HAS ISSUED A WINTER
WEATHER ADVISORY FOR SNOW AND BLOWING SNOW...WHICH IS IN EFFECT FROM
1 AM EST /MIDNIGHT CST/ SUNDAY TO 1 PM EST /NOON CST/ MONDAY.

* TIMING: AS COLD AIR FILTERS IN BEHIND THE COLD FRONT TONIGHT
RAIN WILL CHANGE TO LIGHT SNOW. SNOW WILL TAPER OFF BETWEEN 7AM
AND NOON EST SUNDAY MORNING AS DRYING MOVES ACROSS THE REGION.
SNOW CHANCES WILL INCREASE AREA WIDE SUNDAY AFTERNOON THROUGH
MONDAY MORNING AS PRECIPITATION WRAPS AROUND THE UPPER LEVEL LOW
PRESSURE SYSTEM.

* MAIN IMPACT: LIGHT SNOW ACCUMULATIONS OF UP TO HALF AN INCH WILL
BE POSSIBLE OVERNIGHT TONIGHT. AN ADDITIONAL ONE TO THREE INCHES
OF SNOW IS POSSIBLE ACROSS THE AREA SUNDAY THROUGH MONDAY
MORNING. LATE SUNDAY NIGHT AND EARLY MONDAY MORNING WINDS WILL
INCREASE TO 20 TO 25 MPH WITH WIND GUSTS OF 30 TO 35 MPH. THIS
WILL CAUSE BLOWING SNOW WHICH MAY REDUCE VISIBILITIES AT TIMES
CAUSING TRAVEL DIFFICULTIES.

* OTHER IMPACTS: TEMPERATURES WILL FALL QUICKLY BEHIND THE FRONT
TONIGHT. A WINTRY MIX WILL BE POSSIBLE BEFORE THE PRECIPITATION
CHANGES TO ALL SNOW OVERNIGHT. IN ADDITION ANY WATER REMAINING
ON AREA ROADS OVERNIGHT COULD FREEZE FORMING BLACK ICE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER WEATHER ADVISORY FOR SNOW MEANS THAT PERIODS OF SNOW
WILL CAUSE PRIMARILY TRAVEL DIFFICULTIES. BE PREPARED FOR SNOW
COVERED ROADS AND LIMITED VISIBILITIES...AND USE CAUTION WHILE
DRIVING.

A WINTER WEATHER ADVISORY FOR BLOWING SNOW MEANS THAT
VISIBILITIES WILL BE LIMITED DUE TO STRONG WINDS BLOWING SNOW
AROUND. USE CAUTION WHEN TRAVELING...ESPECIALLY IN OPEN AREAS.

(12-11-10) Winter Storm Update

The deeping low pressure system has now brought widespread rain to to Southern Indiana area. As the low continues to strengthen tonight, expect a drastic change in temperatures to come after midnight. The latest 0Z and 12Z GFS Model Runs are still indicating a dry slot forming just after the passing of the cold front somewhere close to midnight tonight. This dry slot should keep snow accumulations down to a minimum for us. If current predictions in the models hold up, we should get up to one inch of snow tonight and a little more from wrap around moisture on the day Sunday, with lingering snow showers into Monday. It looks like 3" is the absolute maximum we could get with this system unless something drastic changes and it really looks like 1-2" would be much more reasonable at this point. In looking at some other sources of weather info, it looks the the Louisville National Weather Service will be issuing a Winter Weather Advisory later today. Dubois County is the farthest county west in their warning area, so we'll likely be under it and it may be possible that Spencer, Pike and counties to our west will not be since they are in the Paducah NWS office's warning area. Regardless of whether an official Advisory is issued or not, please take caution. This is a potent storm that heeds our attention.

A timeline of what to expect from this system is below:

The cold front will pass somewhere around mindnight-1am tonight, ushering in bitter cold temperatures with it. During the day on Sunday, expect widespread snow showers to form and blustery conditions. Winds will be from the Northwest at 15-25mph sustained, gusting into the 30s! This could create hazardous road conditions if enough snow falls and is blown around. In addition, expect wind chills to be in the single digits to below zero as temperatures steadily fall throughout the day on Sunday as we head to an overnight low of 13. Winds will continue to be sustained in the 20 mph range on Monday as we only rebound to a high of 19 before dropping back to 9 Monday night!

Next week looks to be unseasonably cold, with highs only rebounding to near freezing by Wednesday. Another round of wintry weather could come into play on Thursday, but it does not appear to be as strong a system. I've only forecasted a 30% chance of rain/snow mix at this point. I'll have more on that system as we get closer to Thursday. Here's your updated 7-Day Outlook:

(12-10-10) Updated Snow Forecast

With the last two model runs, it now appears that the Low will indeed move farther to the north in Indiana, which will decrease our chances for large amounts of snow accumulation. As seen in the graphics below, the main bulk of accumulation will be in Northern Indiana and Michigan. The left image is from the 12z GFS Model and the right image is the 12z NAM Model from today. Purple indicates 1 inch, blue 2 inches, yellow 3 inches, light green 4 inches and so on.

While the models don't agree fully on the amount of snow in our area, what is certain is we will get something. It likely won't be much, but with winds on Sunday gusting to 30-35mph as this strong low pressure moves to the north and east of us, blowing snow which can make dangerous road conditions will come into play.

So what about timing? Right now it looks like Saturday will be an all rain event with temperatures peaking into the 40s during the afternoon hours. A strong cold front with this deeping low moves towards us during the daytime and should be moving through the area late Saturday night.

As seen in the graphic at left the 540 thickness line (the rain/snow changeover line, first blue line on these graphics) is just to our west at 7pm on Saturday. It moves well past us by 1am Sunday morning, indicating the passing of the frontal system. What this means is that any precipitation after say midnight on Sat/Sun will fall in the form of snow. And it appears that there will be an ample amount of wrap around moisture from this deepening low to provide some accumulation.

The GFS Model is also showing a dry slot moving through just after the front passes. This may mean that accumulations could be lighter during the overnight hours and we may see the bulk of the snow accumulate during the wrap around moisture on Sunday. This would lessen our totals, but some models are not showing this dry slot. We'll have to see how it pans out.

So what does this mean for us? It looks like we should see somewhere in the range of 1-3" across our area, with more to the north and less to the south of us. Based on current model data, this seems the most conservative estimate. If the low moves a little more south than expected, these totals could rise, but the models aren't indicating that at the time. Temperatures will take a significant plummit overnight on Saturday into Sunday and it appears that we will be in the upper to mid 20s by daybreak with falling temps throughout the day on Sunday. Look for a low in the mid teens on Sunday night.

I've posted an updated snow prediction map of my own below. I'll have more on this as the system gets closer.

Updated 7 Day Forecast

(12-9-10) A Tricky System to Forecast!

If you've been following the forecast for the past few days, you will no dobut have seen much variation in what is expected to fall on our area over the weekend. The graphic at left shows the reason why.

Depending on which model you go with, different results are given. Most models were predicting a more southerly track and the latest models are now taking the center of the incoming Low pressure area about 200 miles more north than they were taking it! Keep in mind that this is only one model run showing the far north scenario and should be taken lightly at this point. We'll need to wait to see if future runs show this or if it goes south again. It could just be a hickup in the data.

I still like the GFS Model Run from 0Z on Wed. It seems to be a reasonable scenario among all the differing models. This run takes the Low through the center of Kentucky and into Ohio, shown on the yellow line in the graphic above. The top blue line shows the varying northerly track given by the latest 0Z model run last night. The bottom blue line shows the more southerly track, which some models have also hinted at. This track would result in a major snow storm for us, but seems unlikely at this point.

So what's the take away from all of this? At this point, I am going to forecast rain on Saturday with highs in the 40s. That rain will change over to snow during the overnight hours into Sunday morning, with lingering snow throughout the day on Sunday. At this point, snow accumulations appear to be minor for Huntingburg, somewhere in the 1-3" area. I'd say three would be pushing it if this track holds out.

The big story may not be the snow coming our way, but the winds that will be associated with this deepening system. Some models have the Low moving into our area near the 999mb range, which means there will be quite a steep pressure gradient associated with this system. The steeper the gradient, the stronger the winds. Sunday will turn out to be quite a blustery day and if the models hold up, it's looking like we could see winds sustained in the 20+mph range, with gusts into the 30s. Whatever snow we do get will get blown around, making driving conditions unfavorable.

I look for winter weather advisories to be issued in the next couple of days. Once the models runs come out tonight, I'll have a better idea of how this system is shaping up. Right now the initial wave is in the Pacific Ocean, moving into the Northwest Coast area. With few weather buoys in the area, once the system moves on shore and more data points are available for entry into the models, look for us to have a much clearer picture of what is going to happen. In the next 24 hours we would be able to start fine tuning the forecast and getting a clear picture of the tracking and the potential snow totals. I'll update more once the next models come out.

Reviving This Blog

With winter fast approaching, I am planning on reviving this weather blog as best I can. I had let it go due to time commitments, but I am wanting to post as often as I can, and especially during winter weather storms. You'll be able to read my analysis and predictions of upcoming of weather events as I post. It looks like a major storm is coming in this weekend for someone in our area, but it is unclear who will receive the bulk of the snow at this time. I'll be posting an update soon.