Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 8:43 PM GMT on December 19, 2007
Good morning. Today a powerful cold front will move through the area with heavy rain and high winds. A wind advisory and some high wind warnings are out for all of Pennsylvania. Also the spc has highlighted central and western pennsylvania for a slight risk of severe thunderstorms. The will be a low topped squall line which will form and possible have some miniature supercells with some rotation too. This will also be something to watch. After the front moves through the lake effect machine fires up with snow in the northwest.
Severe Weather Outlook...
"Short Term Forecast"
Currently here in Harrisburg it is 53degrees with low clouds (ceiling about 700'), light rain, and fog (visibility about 1.5miles). Today could be interesting across the state with a narrow band of extremely heavy rain and a possible embeded thunderstorm. We could see some very high winds with the frontal passage in excess of 50mph for a hour or two. Also dropping temperatures will result in a few hour period of snow across the western half of the state. Expect no snow across the eastern half. Rain totals statewide should be about 1inch. Snow totals from front should be about 1inch across the north and west. Also lake effect will begin after the front and drop several inches in typical snow belts.
*More updates coming throughout the day...
*High Wind Warning* for central Pennsylvania
*Wind Advisory* for northeastern Pennsylvania
*High Wind Warning* for extreme northwestern Pennsylvania
*Wind Advisory* for western Pennsylvania
*High Wind Warning* for southern Poconos
*Flood Watch* for eastern Pennyslvania
Christmas looks to remain cloudy across most of the state with some flurries in the northwest and southcentral. Also throughout next week are chances for small precipitation chances with small fronts. Rain during day and snow during night can be expected. Highs will remain seasonable until this weekend with the next major storm. Many questions remain with that storm. Track will play a major part in precipitation types. Also the 12z run of the GFS shows a coastal storm on New Year's Day with snow affecting the entire state. This will be something to watch, because this is also when the NAO goes negative again. Check out this model run for the January 1 storm...
So here is my christmas day forecast...
Eastern- (Allentown, Southern Poconos)-
Mostly cloudy and cold. High 40. Low 27.
South Central (Harrisburg, York, Lancaster)(my home)-
Cloudy and cold. Passing flurry. High 39. Low 27.
Partly cloudy and cool. High 45. Low 30.
Central- (State College)-
Cloudy and cold. High 34. Low 21.
Northern- (Bradford, Williamsport, Erie)-
A few snow showers. (coating of snow)High 32. Low 21.
Cloudy and cold. A few snow showers. High 36. Low 26.
A few snow showers. (coating of snow)High 31. Low 23.
Here is todays NAO...
**Just to throw out there...
The EURO model and GFS model have extremely different scenerios for the weather after about Wednesday. Personally I do not think we can trust either model. Also the GFS develops a relatively strong coastal storm on Thursday, but it stays far enough off shore not to cause an impacts. We still though should watch the track, in case of any changes will have a dramatic impact on the coastline of the middle atlantic and new england.
***Update as of 200pm
Check out that mean looking squall line near Latrobe, PA.
It developed right behind that small dry slot. The squall line will probably contain very heavy rain along with isolated gusts to 65mph. I will have continuing updates on the severe weather throughout the day across Pennsylvania.
MESOSCALE DISCUSSION 2260
NWS STORM PREDICTION CENTER NORMAN OK
0111 PM CST SUN DEC 23 2007
AREAS AFFECTED...CENTRAL/ERN PA...CENTRAL NY...NRN DELMARVA
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 231911Z - 232045Z
LINE SEGMENTS OF CONVECTION HAVE RECENTLY DEVELOPED IN WRN PA AND
WIND DAMAGE THREAT WITH THESE STORMS MAY INCREASE AS THESE LINES
MOVES EWD INTO CENTRAL/ERN PA...CENTRAL NY AND PERHAPS EXTEND AS FAR
SOUTH AS NRN DELMARVA. A WATCH ISSUANCE IS A POSSIBLE SOON.
CONVECTION IN WRN PA IS CURRENTLY LOCATED ALONG STRONG COLD FRONT
THAT IS MOVING RAPIDLY EWD THROUGH THE REGION. INSTABILITY IS
EXTREMELY WEAK...BUT ENVIRONMENTAL WINDS ARE EXTREME WITH 50-70 KT
WINDS LOCATED LESS THAN 1 KM ABOVE THE SURFACE. AT THIS TIME...THE
WINDS ABOVE THE BOUNDARY LAYER ARE PREDOMINATELY SLY...WHICH IS
PARALLEL TO THE N-S ORIENTED LINE SEGMENTS. HOWEVER...A 100 KT JET
STREAK LOCATED AT 500 MB WAS LOCATED OVER KY AT NOON AND IS FORECAST
TO NOT ONLY INCREASE THE MID LEVEL WIND SPEEDS...BUT ALSO AID IN
VEERING THE WINDS ABOVE THE BOUNDARY LAYER TO MORE WLY AND
PERPENDICULAR TO THE LINE SEGMENTS. THE WILL LIKELY ACCELERATE THE
LINE SEGMENTS MORE RAPIDLY EWD AND ALSO ENHANCE THE POTENTIAL FOR
THE STRONGER WINDS ALOFT/DAMAGING WINDS TO REACH THE SURFACE. THE
JET MAX IS FORECAST TO BE LOCATED IN WRN PA BY 21Z...WITH INCREASED
THREAT OF WIND DAMAGE WITH LINE OF CONVECTION MAY EVOLVE SOON.
DESPITE THE CONVECTIVE NATURE OF THE LINE SEGMENTS...THE WEAK
INSTABILITY MAY LIMIT THE VERTICAL DEPTH OF CONVECTION AND ONLY VERY
ISOLATED LIGHTNING IS EXPECTED.
A High Wind Warning has been issued now for most of central Pennsylvania replacing the wind advisory. The squall line looks like it weakend but it may restrengthen when it hits 60degree air here in the central Pennsylvania area. Stay tuned for furthur updates through this afternoon and evening. Also I noticed light snow is being reported in Erie after they were at 53degrees earlier today. So there is a dramatic temp. drop off after the front goes through.
Well the front blew threw Harrisburg PA with some trees and power lines down near Middletown. It is now windy with falling temperatures. Lake effect snow will start in snow belt regions as soon as the winds shift from the southwest to the west. Check out the model run for the 2 of January. It has a major coastal storm with lots of snow. This will be something to watch.
This is the format I will give forecasts for the State of Pennsylvania for normal days unless a major storm is expected.
Afternoon thoughts, Short term, Long term, Just to throw out there, and last any updates needed
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
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