Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 2:06 PM GMT on November 09, 2008
"Afternoon Thoughts" (Updated 11/09)
So yes here it is already the unofficial end of Fall in my book. Leaves are just about gone out of most of the trees except for a few lone yellow oaks. Mountain has quickly turned brown and countryside looks drab with fields of brown. With temperatures last week in the 60s in low 70s it certainly did not seem like the end of Fall. For the first eight days of November temperatures were above normal except for the 2nd here in Harrisburg. The positive temperature anomaly is 6.3degrees here in Harrisburg with a max of 70degrees and a min of only 46degrees. But things are changing. A trough has blow into the region with more seasonable temperatures and even below normal temperatures helping to cut back on those positive averages.
Alrighty my last blog I ranted about the inaccurate climatology readings from area weather stations. So this blog I want to talk about weather service forecast low temperatures. This has bothered me for quite a long time with how inaccurate temperatures are for low temperature predictions. It seems that almost every night temperatures are colder than predicted by local weather services. Now I do understand that the suburb and rural locations are colder, but still even in the city locations temperatures are always colder. It does not seem meteorologists take into account the full effects of radiational cooling especially in Pennsylvania. Radiational cooling has some impressive effects in Pennsylvania thanks to the deep valleys between the mountains. As the sunsets, cold air goes rushing down the mountainsides. During the day higher elevations have cooler temperatures and the equilibrium pull pushes the colder temperatures down the mountainside into the valleys. With now clouds there is no cover to keep the warm air insulated so the warm air rises and colder air sinks. When the winds decouple (calm) temperatures are allowed to fall. Typically temperatures get about as low as dewpoint values are, but during best of radiational cooling nights dewpoint values may also fall. Sometimes I found forecasts for low temperatures are off by 10degrees, but yet I am only in the suburbs, so even the rural locations are colder than I am. I just wonder why especially local forecasts cannot take account prime radiational cooling conditions. Rarely do low temperature forecasts bust on the cold side. So overall I was just wondering if other people have the same experiences I have with low temperatures being much colder than forecast even with point and click NWS forecasts?
"Current Surface Plot"
(Courtesy of HPC)
(Courtesy of Wunderground)
(Courtesy of NOAA)
"Forecast Discussion" (Updated 11/09)
A relatively amplified jet remains parked across the nation with a trough in the east and a ridge in the west. Several deviations below normal, the 850s drop to near -8C across northern Pennsylvania with a westerly cyclonic flow during the day Sunday and Monday. Westerly winds will draw up moisture from the lakes and keep a stratus deck over the Allegheny Mountain region east to the Ridge and Valley region. Surface temperatures will remain below normal for Sunday and Monday. Flow becomes capped off from lakes by late Monday evening with flurries being the only precipitation scattered about the region. By Tuesday a 1028mb high pressure moves across the region making for Sunshine across the region. High temperatures remain below normal. An occluded front moves north across the region with rising heights to near 0C around the I-80 corridor. A low stratus deck moves over the region for Wednesday with the chance of some flurries or sleet pellets across the southern part of the state as some light precipitation with QPF around .01inches is forecast. High pressure moves off to the northeast with building heights over the east near 10C. Trough moves in from the Great Lakes with coldest air of season poised to moves across the Pennsylvania towards the weekend. For Thursday light rain is expected over the region, with mild temperatures in western Pennsylvania back up into the 50s. But with 1028mb high pressure northeast of region some cold air damming will keep temperatures in the 40s in eastern Pennsylvania. All precipitation will remain rainfall. Then some questions arise as we head towards Friday. GFS wants the trough to tap into the southern branch of the jet stream forming a strong low pressure system dumping heavy rain across the region for Friday and Saturday while the EURO and CMC take a more moderate route with just a typical frontal passage followed by colder air. But some of the ensemble models also have a similar solution to the GFS. 0z GFS solution on Saturday showed the 988mb low pressure heading straight up through the Appalachians, which is not a typical storm track. 12z Saturday CMC sort of showed a more coastal solution while the 18z GFS Saturday run showed a solution with a low pressure headed up through Michigan. In any case heavy rain does look possible for Saturday with H85s near 10C and PWATs several deviations above normal. QPF may be in excess of 1inch if the trough can tap into the southern jet. A lot of variables need to be modeled out for the late in the week system, so forecast for weekend remains pretty questionable. I sort of like the storm track solution up through the eastern Great Lakes with heavy rain up the east coast, followed by the frontal passage. After the front moves through the coldest air of the season overtakes the region with lake effect snows. 850s fall once again below 0C.
(Courtesy of Penn State Meteo.)
"Current Water Vapor Loop"
(Courtesy of Penn State Meteo.)
"Weekly Forecasts" (Updated 11/09)
Monday- After shortwave moves over region Sunday night, some snow shower and flurries will be about the region especially during the morning hours. Stratocumulus will be around much of Pennsylvania during the afternoon hours with snow showers towards northwestern Pennsylvania. Snow accumulations will generally be near one inch. Winds will be westerly at times gusting to 30mph, especially on the ridge tops. Highs will be very cold with them in the low 30s across the northern mountains and elevations above 2000ft. Upper 30s to low 40s can be expected in western Pennsylvania, mid 40s in central Pennsylvania, and upper 40s in eastern Pennsylvania. Downsloping winds will turn eastern Pennsylvania sunny in the afternoon towards dusk. Snow showers will end by early evening and debris clouds will float around central and western Pennsylvania. Winds may calm down Monday night making for some very cold temperatures as dewpoints may be in the low 20s. Lows may be in the 20s statewide with low 20s across northeastern Pennsylvania valleys.
Tuesday- High pressure dominates the weather over the region with only a few flurries expected over northern Pennsylvania during the morning hours. Winds will shift west-northwesterly and the stratocumulus deck should break giving way to widespread sunshine across the entire state during the afternoon. Highs will be the coldest day of the week with most areas not making it out of the 40s even with brilliant sunshine. Highs may stay in the upper 30s for all elevations above 2000ft. Clouds from the west will be approaching the western Pennsylvania region by desk as an occluded front moves into the region. Lows will be in the mid 30s across western Pennsylvania, low 30s across central Pennsylvania, and upper 20s in eastern Pennsylvania. After midnight some light sleet/rain will move in across western Pennsylvania gradually turning to all rain. Precipitation amounts will be less than .1inches.
Wednesday- Any leftover rain showers should fizzle out over the mountains while trying to move eastward. Mostly cloudy skies will dominate the entire state during much of the day Wednesday keeping a cap on temperatures rising. Also high pressure to the northeast will keep eastern Pennsylvania region cold air dammed. Highs in western Pennsylvania will be in the upper 40s, in central Pennsylvania in the upper 40s, and eastern Pennsylvania in the mid to upper 40s. A few flurries cannot be ruled out in the northeastern mountains during the day Wednesday. By Wednesday night precipitation will advect into southwestern Pennsylvania and overspread the entire state. As temperatures aloft and boundary level in parts of northeastern Pennsylvania, there could be a rain/snow mix with no snow accumulations. But by later in the night any snow should turn over to all rain. Rainfall amounts will be less than .25inches. Lows will be milder than past nights with them in the 40s statewide, except for the northeastern mountains, which will be in the 30s. Some fog may form on the ridge tops later at night as ceilings drop to 1000ft.
Thursday- Rain showers and clouds will dominate the weather over the state of Pennsylvania as a cold front approaches the region with low pressure moving up from the south advancing gulf moisture northward. Rain will generally be showers in nature with rainfall amounts less than .25inches with the heavier amounts in southwestern Pennsylvania. Highs will stay cool as high pressure remains to the north keeping temperatures statewide in the upper 40s to low 50s. Some southern areas in York, Lancaster, and Philadelphia though may squeeze out some mid 50 readings as winds begin to shift to the south. Later in the day winds may become breezy as winds aloft and increase and at times migrate to the surface. Winds should be out of the southwest and no more gusty than 30mph. Fog will be over the ridge tops as ceilings will be low during the day with a stratus deck. By evening rainfall will increase over the region and become steadier and increase to a moderate intensity. Lows will be quite mild in the low to mid 40s across the state and should not move much from daytime high temperatures. Rainfall amounts will generally be less than a half an inch during the nighttime hours. Winds will be gusting up to 25mph at times.
Friday- Low pressure will be closing in over the region with the front advancing eastward through the Ohio Valley. Temperatures aloft soar, but boundary layer temperatures remain slower to respond with highs generally in the mid 50s in the mountains and low 60s across elsewhere in the state. Rainfall may turn more convective in nature and cellular with pockets of very heavy rain. Rainfall amounts should generally be less than .5inches statewide with the heavier amounts in western Pennsylvania. Winds will again be gusty out of the southwest to at times 35mph along the Laurel Highland ride tops especially. By Friday night the front will be moving in towards western Pennsylvania with rainfall now falling in a large band and plume of moisture. This band of moisture will slowly progress over the state with rainfall amounts less than .5inches. Low temperatures will be quite mild Friday night and possibly in the low 50s in southeastern Pennsylvania with upper 40s elsewhere. A lot of questions remain with the Friday forecast, so a Saturday forecast will not be issued until the date becomes closer to the event. Stay tuned.
"Current River Ice Reports and Ski Conditions" (Updated 11/09)
Still another three weeks before ski resorts begin to open up across Pennsylvania and before the snow pack begins to build up in the snow belts. This time of year it can snow but usually the cold weather is followed by mild air quickly melting any snowfall. There is though a building snow pack across some of the mountains in New England, especially Mt. Washington where already nearly a foot of snow has fallen and not completely melted. No river ice probably for more than a month across most waterways, but water temperatures are definitely falling even into the upper 40s across some mountain lakes in the north country near Bradford; most water temperatures including Lake Erie are in the low to mid 50s. These temperatures are cold enough for hypothermia if fallen into the water during a cold night with temperatures below 40degrees, so please act responsibly when near waterways this time of year.
Ski Sawmill... 12/08
Ski Liberty... 12/05
Shawnee Mountain Ski Area... 11/29
Camelback Ski Area... 12/05
Blue Mountain Ski Area... 12/05
-Link to official reports page from NWS...Link.
-Link to local ski resort snow conditions...Link.
"Current Northeast Snow Depth and Northeast Windchills"
(Courtesy of Wunderground)
"Lake Effect Snow Conditions" (Updated 11/09)
A relatively minor, nuisance type lake effect snow event is headed towards northwestern Pennsylvania Sunday night through Monday morning. A secondary, undefined cold front will move through Sunday afternoon to reinforce the cold air. Followed behind that is H85 temperatures of nearly -10C. Looking at some of the recent data in the Midwest it appears that temperatures aloft are slightly colder that be currently progged by recent GFS model runs such as the Saturday 12z. Thickness 1000-500mb looks pretty cold enough for snow for elevations above 1000ft for Sunday night. With cooling columns overnight I would not be surprised to hear some valley snow flurries and coatings about as far east as the ridge and valley region. Flow is not too great with about a 270 westerly vector. But it looks enough for a decent fetch into the Laurels and Northwestern Mountains. Looking at CAPE levels they are about 50-100 j/kg nearest to the lakes along with some decent Omega growth for decent snowfall crystal growth. With some of the decent CAPE, some thunder snows cannot be ruled out. Downsloping winds should keep snow showers and flurries confined to mainly the mountainous terrain, but early Monday morning snowflakes may make it east of the Blue Ridge. Snow accumulations will remain pretty much of a nuisance, as ground temperatures are very warm from the recent mild spell. Favorable snow belts in southwestern Erie and Crawford Counties, Warren County, should be able to squeeze out 2-4inches of snowfall in the highest ridges with elevations above 1900ft. Valley locations should just be dealing with C-2inch type amounts. Some of the latest short models such as the SREF and NMM models show that a pretty decent band could form through Crawford, Erie, Warren, and McKean Counties as the flow is westerly. The highest accumulations should be found in this region. Lakeshore regions near Erie will stay mostly rainfall with some graupel mixed in at times maybe coating the ground. By early Monday evening flow looks to be capped off with drier air moving in with light and variable winds thanks to a 1024mb high pressure. By Tuesday it appears the region will be under sunny skies. As for lake enhanced precipitation it appears that the flow will be cutoff for the rest of the week until next weekend after a large cold front moves through the region. But details are nil to none at this time.
Snow Map for Lake Effect Accumulations from Sunday to Monday Night...
"Current Lake Erie Wind Direction and Speed"
(Courtesy of NOAA)
"Current Lake Erie Water Temperature"
(Courtesy of NOAA)
"Long Term Outlook" (Updated 11/09)
We have about two more weeks before looking into decent snow chances in the long-term section, but for now we can try to look for any possibilities as we are already past the first week of November. But I am relatively pleased with the pattern I see shaping up for mid to late November, but there are a few worries of mine too. Looks like a full pattern changing type system will be headed this way towards this weekend. GFS brings in an impressive system with heavy rains and wrap around snows. Then as cold front departs a cutoff low forms up in Canada keeping instability snow showers and flurries around for the beginning of that week along with extremely gusty winds. Mostly likely a lake effect snow outbreak potential would occur and be pretty widespread, as latest guidance wants to keep flow relatively favorable for an extended period of time. Latest EURO anomalies also favor a very deep trough over the region with quite cold temperatures keeping highs in the low to mid 30s across the north and low to mid 40s across southern Pennsylvania. Some of the GFS model runs have been extremely cold for this time period with for some reason the 0z runs being colder than the 12z runs. But it does seem a general consensus for the 850s to be near -10C as far south as the Mason-Dixon line. Now the question remains is how progressive will the pattern be. The EURO weeklies seem to want to have the colder weather stick around through the end of the month while the GFS has been back and forth with model runs between progressive troughs lifting in and out or a consistent deep eastern trough. I have yet to see solid guidance to indicate either scenario until I see evidence for a development of Greenland Blocking. The Saturday 0z GFS showed extreme below normal temperatures over the eastern United States towards the 20-beyond period with temperatures below freezing for high temperatures for most of Pennsylvania according to the 2m Charts with temperatures aloft near -15C. But then the 12z GFS Saturday run showed a progressive pattern with troughs and below normal temperatures between zonal flows with average temperatures. Looking at teleconnections the NAO is forecast to remain neutral to slightly negative, which is usually a pretty good sign for eastern below normal temperatures and the PNA will be from neutral to slightly positive favoring a ridge in the west. One major index I am looking at is the AO, which is forecast to head negative for the first time in quite a while. Now there is no definite correlation for the AO as sometimes when it heads negative the polar air is pushed towards Asia, but other times it can be pushed towards the United States. From some of the indicators I think it should bring a push of colder air to the United States towards the end of November into December. I like chances of snow potential around Thanksgiving or so. One thing that does look pretty likely is that an extended period of mild temperatures does not look likely anywhere in the near future. Overall it appears an extended period of below normal temperatures is possible through mid to late November. So for the short term each trough will reinforce the one before it before a final push of cold air heads towards the region around the 18th.
"Current NAO and PNA Predictions"
(Courtesy of NOAA)
"Monthly Outlook" (November)
So hard to believe October has already passed, but it has and we are now entering November. Looking at my October outlook I called for normal to slightly below normal temperatures with normal precipitation. Looking at most official climate stations most areas came in with below normal temperatures around 1-2degrees below normal. I am very pleased with my temperature forecast, but as for precipitation almost all areas were below normal in precipitation and many areas did not see rain until the last few weeks in the month. It seems the Fall season has been pretty dry in consideration to normal. Snowfall was highly above normal in all locations with snowfall totals over a foot in parts of the Poconos and areas in western Pennsylvania saw record monthly snow totals including Pittsburgh which I believe saw the 8th snowiest October on record. Looking at now November there are some better signals for the temperature and precipitation totals than there were last month. Last month there were few signals for the overall pattern.
Temperature- Temperatures look to be near normal across much of Pennsylvania, except southern Pennsylvania which should see below normal temperatures. Across other parts of Pennsylvania I cannot rule out some slightly below normal reports. It seems that the first half of the month will favor above normal temperatures, but clouds from marine layers in an easterly flow will keep temperatures closer to normal in the south. The positive temperature departure should be much higher in the north and west than in the south and east come mid month. By midmonth teleconnective signals are showing a dive-bombing AO along with a positive PNA and a negative NAO. I am thinking the second half of the month will be very cold and that pattern should continue through December. Looking like some nice Greenland Blocking will develop. EURO weeklies and GEFS indicate this pattern switch come midmonth, but the operational GFS is a bit slower to show this pattern change. So overall looking at normal to below normal temperatures statewide.
Precipitation- I think precipitation will be near normal. I am looking at a more active storm track than recent months, but still not anomalous in comparison to normal. Coastal storms look possible along with warm air advection events especially near the pattern switch come midmonth. Snowfall looks to be near normal with almost all areas likely seeing their first accumulating snow before the month’s end. Lake effect snows look possible along with some nuisance clipper type events. Looks like snowfall will be in quite a positive start in comparison to normal for parts of eastern and western Pennsylvania as we head into the start of winter.
"Temperature and Precipitation Outlooks from Climate Prediction Center for next 30 days"
(Courtesy of NOAA)
-Winter 2008-2009 forecast... Link.
-Winter 2008-2009 forecast update... Link.
"Here northeast of Harrisburg 2008-2009 winter statistics"
Current Snow Cover- 0.00inches
Monthly Total- Trace
Seasonal Total- Trace
Winter Weather Advisories- 0
Winter Storm Warnings- 0
Heavy Snow Warnings- 0
Blizzard Warnings- 0
Snow Advisories- 0
Winter Storm Watches- 0
Lowest High Temperature- 43
Lowest Low Temperature- 26
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Snow Storms Stats)
First Snow - October 29 - Trace
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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