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Wed Jan 30, 2019, 02:01 PM

Pennsylvania Min Temps 1/30/19: Topographic Impacts

Noticed this this morning and figured I'd share.

Anyone in PA knows that Bradford, PA has a reputation for unusually cold temperatures and typically has the lowest temperatures in the state thus it's nickname: Ice Box of Pennsylvania. Part of the reason for this is the Bradford Airport where the National Weather Service takes it's official reading sits well outside of Bradford on top of some relatively exposed terrain. But heigh elevations and exposure don't necessarily yield the lowest temperatures. The NWS temperature summary for last night shows that the lowest recorded temperature in PA was at the York County Airport near Thomasville, PA, which is between Baltimore, MD and Harrisburg, PA. Last night's low temperature at Bradford was -3 F but at Thomasville, PA it fell to -5 F.

From NWS PA Summary: https://forecast.weather.gov/product.php?site=NWS&product=RTP&issuedby=CTP


MAX/MIN TEMPERATURE AND PRECIPITATION TABLE FOR PENNSYLVANIA
NATIONAL WEATHER SERVICE STATE COLLEGE PA
745 AM EST WED JAN 30 2019

:Automated Surface Observing Systems (ASOS) Sites
:Automated Temperature and Precipitation Data -
:24 Hour High/12 Hour Low Ending 7 am EST/8 am EDT and
:24 Hour Accumulated Precipitation Data ending at 7 am EST/8 am EDT
ennsylvania -- Temperature and Precipitation Stations
:......................................................
: Station Max / Min / 24-Hour
: Name Temp/ Temp / Precip
:......................................................
:

ABE : Allentown : 32 / 12 / 0.28
AOO : Altoona : 30 / 12 / 0.06
BFD : Bradford : 27 / -3 / T
CXY : Capitol City : 31 / 9 / 0.12
FIG : Clearfield : 28 / 0 / 0.04
DYL : Doylestown : 37 / 14 / 0.16
DUJ : Dubois : 30 / 5 / T
ERI : Erie : 37 / 5 / 0.01
MDT : Harrisburg : 31 / 11 / 0.17
JST : Johnstown : 31 / 9 / T
LNS : Lancaster : 35 / 7 / 0.22
GKJ : Meadville : 35 / 1 / T
MPO : Mt. Pocono : 28 / 4 / 0.21
PNE : NE Philadelphia : 43 / 19 / 0.20
PHL : Philadelphia : 43 / 20 / 0.16
AGC : Pittsburgh : 42 / 7 / T
PIT : Pittsburgh Intl : 43 / 7 / T
PTW : Pottstown : 34 / 6 / 0.32
RDG : Reading : 31 / 11 / 0.20
AVP : Scranton : 30 / 8 / 0.25
SEG : Selinsgrove : 30 / 2 / 0.07
IPT : Williamsport : 30 / 6 / 0.05
THV : York : 32 / -5 / T


What gives? What you are seeing is the impact of new snow on the ground, clear skies and topographic induced cooling. The Thomasville Airport (THV) sits at a slightly lower elevation than the surrounding area. With new snow on the ground, clear skies and little to no wind the surrounding area radiates heat very efficiently causing cold air to sink into the low spots in the terrain creating pools of cold air. For contrast, the Thomasville Airport's closest NWS stations are Lancaster, Capital City and Harrisburg (International Airport). Those stations bottomed out in the low teens to upper single digits, over 10 degrees warmer than Thomasville. I've seen this local temperature discrepancy in all seasons. If the air is calm and the skies are clear it's not uncommon for Thomasville to be 10-20 degrees cooler than the surrounding area.

Kind of neat. Thanks for looking and stay warm!

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