Daweathablog

Charles E. Roop giving his own forecasts, weather discussions, photos and adventures for the Starkville, MS area, Florida, and beyond.

Thursday, January 7, 2010

Snow? Here?

For the last few days, most of the United States has been plunged into the deep freeze as a persistent synoptic pattern keeps funneling cold Canadian air southward. For Florida, this trend is expected to continue well into early next week.

For the last few days, abundant discussion on social networking sites and around the proverbial water cooler have been on the $60,000 question: Will it snow in Florida? To most, it would seem like it given that it's been so cold for so long in this state.

Synopsis

An Alberta Clipper system (what's that?) and it's associated front, which is currently over the lower and middle Mississippi River valley, is bringing snow from Wisconsin to northern Mississippi and Alabama while bringing rain for central and southern Mississippi and Alabama and most of Louisiana. High pressure currently remains over the Florida panhandle. This helped keep the winds relatively calm overnight and skies clear to allow temperatures to fall to near-record territory across the state.

Preliminary figures from the NWS suggests that the low in Gainesville this morning was 21 degrees, which would break the old record of 22 set back in 1924. It may have been as low as 21 in Ocala, as well.

At the upper levels, a trough in the jet stream is beginning to fold in the upper Plains and New England while the subtropical jet stream passes over Florida. This may have aided in keeping south Florida mostly cloudy this morning (judging by infrared satellite imagery) and staving off colder weather for that area.


Jet Stream analysis from 1 a.m. ET today (left) and surface analysis at 7 am ET (right).

Later Today through Saturday.

Short-range forecasts from the HPC show the storm system moving east as the high over Florida now moves east. Early Friday morning, the front is expected to be over the panhandle and and be over central Florida at around 7 a.m. The front should be over south Florida by the end of Friday evening.

There are a few things to keep in mind. For starters, will it even be at or close to freezing at the time precipitation will pass through. One tip given (via Weather Prediction) is to see if temps are below freezing at the surface and 850-mb levels (Weather recap for the novice: As elevation increases, the pressure decreases). If so, "snow is the most likely precipitation." Also, it
s good to see what type of thermal advection (movement of air horizontally) is taking place.

With those of many tips given, lets look at the models. Remember, models are not forecasts etched in stone and things can change. These are used as a guidance.

The NAM at 7 pm ET Friday is showing spotty and isolated precip around the north central Florida area. I would count this as a slim chance of precip in the area. At this time, the air temps at 850 mb and 1000 mb are close to freezing. As the night wears on, precip increases over central Florida. For 7 am ET Saturday, temps at 1000 mb are at or below freezing for much of the north central and central Florida while the freezing line at 850 mb is around the I-10 corridor.

The GFS' 06-Zulu run shows the precip associated with the front passing through during the afternoon and evening on Friday. The freezing level at 850 mb is to the north of the Florida/Georgia state line at 7 pm ET Friday while the line is moved south to near Gainesville 12 hours later. The 1000-mb freezing line is over central Florida during the model runs for Friday evening and Saturday morning.

Those are two models with slightly different takes on precip and temperature above the surface. What could be the case? I am not too sure about snow for the northern half of the state. I will be really shocked if we do get it. I can say this: There will be a very slim chance of snow for the north central Florida area. It would depend on the timing of the precipitation.

How about sleet? It would be more plausible than snow, I think. Again, it would depend on the timing of the precipitation. If precip falls at night, it could happen. It also depends on thermal advection.

Here's what the National Weather Service in Jacksonville (NWS-JAX) has written in an earlier Area Forecast Discussion:

DUE TO THE SLOWER PROGRESSION OF PRECIP...HAVE ALSO INDICATED SOME
MIXED PRECIP DURING FRI MORNING ACROSS EXTREME SE GA WITH A COLD
RAIN EXPECTED ELSEWHERE. HOWEVER...WOULD NOT BE SURPRISED TO GET
REPORTS OF SOME SLEET MIXED WITH RAIN INTO EXTREME NE FL. NO
ACCUMULATIONS ARE EXPECTED...BUT STILL CONCERNED ABOUT WET ROADS
FREEZING DURING THE EARLY MORNING HOURS ON FRI IN SE GA AS COLDER
AIR FILTERS IN BEHIND THE FRONT. DAY SHIFT ISSUED A SPECIAL WX
STATEMENT ADDRESSING THIS...AND WILL REFRESH THIS PRODUCT WITH THE
LATEST THINKING.

MODELS STILL INDICATING SOME LINGERING MOISTURE OVER THE EXTREME
SE ZONES AS A DISTURBANCE MOVES ACROSS CENTRAL FL EARLY SAT. HAVE
INCLUDED A SLIGHT CHANCE OF RAIN OR SNOW OVER THIS AREA WITH A
SMALL AREA OF FLURRIES BEHIND IT GENERALLY SE OF A ST AUGUSTINE TO
OCALA LINE. AGAIN...MEASURABLE AMOUNTS ARE NOT EXPECTED.

Bottom line: Very, very low chance of snow. Sleet possible depending on temperatures aloft and timing of precipitation. Chances would be greater the farther north you go. However, just as NWS-JAX keeps mentioning in their forecast discussions: "Measurable amounts [of winter precip] are not expected."

The Next 24 Hours

Expect temps to increase slightly today into the 50s for the Gainesville area today with mostly sunny skies. Tonight, things will begin to change with a chance of showers and a low in the low 30s. Based on temp profiles aloft with guidance, I don't see much of a chance tonight for any winter precip. Friday, things will get interesting and may change. I might write another post if updates are necessary. Otherwise, keep any eye on my Twitter feed for the latest at twitter.com/daweathaman.

Friday, January 1, 2010

New Year Brings Cold

Good afternoon and Happy New Year, everyone. It's been a while since my last weather blog post. I am kind of making it a New Year's resolution to make more posts on here - at least once every few days. Hope it sticks.

At the moment, a cold front with associated showers have passed the Gainesville area late this morning. Skies continue to be mostly cloudy, but judging by visible satellite imagery clearing is expected in the area real soon as the cloud cover passes with the front.

At the upper levels, a deep trough in the jet stream, along with the passage of the surface low and its flow, will bring colder air to much of the midwest and eastern U.S. for the next few days according to guidance models. NWS-JAX is considering this as "one of the longest duration cold spells in quite some time" in this morning's Area Forecast Discussion.

However, the big question: How cold? NWS-JAX calls for lows in Gainesville in the low 30s tonight, but MOS guidance is mostly hinting in the upper 20s except for the NAM. I would have to agree with the NWS at this time since, based on experience, it might take a little longer for the coldest air to reach here after the passage of the front. Plus, winds created by pressure gradients after the passage of the low and associated cold front will inhibit radiational cooling and keep air temperatures a little warm. However, with any wind, it may feel colder.

Starting Saturday, the pressure gradient is expected to weaken and bring colder nighttime temps to much of Florida. NAM guidance seems to be treating this a little warm while GFS is calling for temps near 20. For now, I would wait before I call for an exact temperature reading. Regardless, by Florida standards, temperatures are expected to be very cold with below freezing temps each morning through at least Wednesday. Highs are expected to not get close to 60 degrees through Wednesday.

For now, I call for clearing skies in the area today with highs reaching into the upper 50s. Continued clearing with some wind is expected tonight in Titletown with a Saturday morning low near 32. Keep any eye on my Twitter and Facebook feeds for my predictions for the next few nights. Stay warm.