Area forecast discussion 
National Weather Service Pittsburgh PA 
333 PM EDT Sat may 25 2013 


Synopsis... 
dry and cold weather can be expected for the weekend. Warm and 
humid conditions will return by mid-week. 


&& 


Near term /through Sunday/... 
surface high will continue to build over the region as the upper 
low rotates over New England. Tightened pressure gradient flow 
between the two systems will allow for some stronger northwesterly 
winds to continue...although focused a bit further east than 
yesterday. Beyond some scattered diurnal cumulus...some high cirrus 
from a convective system off to the west may make it into the 
western zones. However...most of the forecast areas should see a 
mostly sunny day. Despite the sunshine...cold northwest flow will 
keep temperatures 10 to 15 degrees below seasonal normals once 
again today. 


With building high continuing its progression eastward...expect 
another calm...clear night tonight. However...with the boundary 
layer warming slightly...focus of widespread frost/freeze has 
shifted a bit farther north and east. Did however expand freeze 
and frost products per coordination with adjacent offices and 
relatively low dewpoints remaining over the region. While 
confidence in a widespread freeze in the higher elevations remains 
low...isolated pockets of below-freezing temperatures could 
occur...especially in the more sheltered valleys. 


Sunday should once again be a quiet weather day with temperatures 
moderating a few degrees closer to normal. Wind gusts should 
continue to diminish as high settles overhead. 


&& 


Short term /Sunday night through Tuesday night/... 
as closed low over New England opens and exits northeastward...forecast area 
will remain under influence of ridge. Light winds and clear skies expected Sun 
night and Monday for much of region. As a result...temperatures once again expected 
to drop late Sun night. Freeze watch was issued for northern zones...where 
temperatures forecasted to be very near or blw freezing. With upper ridge remaining to west of 
forecast area through Monday night...very low probability of precipitation were continued through the period. 


Warm front aprchs on Tuesday as upper ridge shifts eastward. Moisture will be slow to 
return to the area...so only low probability of precipitation were maintained through Tuesday 
night. Any precipitation will be tied to timing of low-amplitude shortwave troughs 
that are poorly resolved at this time...but cannot rule out possiblity of a 
thunderstorm given expected warm air advection. 


&& 


Long term /Wednesday through Saturday/... 
upper ridge will amplify over eastern Continental U.S. Remainder of the weak as southwesterly low- 
level flow increases. This flow will provide ample moisture and heat to the 
region. Temperatures in middle-upper 80s expected to return by mid-wk. 


Although low-level moisture will be present...lack of a boundary and 
uncertain sphere of influence of strong upper ridge will lmt precipitation covering. 
Given low confidence in amplitude and northward position of upper ridge... 
probability of precipitation cannot be ruled out completely. With modest instability present... 
slight chance thunderstorms will be carried daily through the extended periods until 
it is clear whether capping/subsidence or heating will win out. 


&& 


Aviation /19z Saturday through Thursday/... 
VFR conditions should continue for the remainder of the day as high 
pressure builds eastward. Northwest wind at 10-15 with gusts to 25 
knots will be possible until after sunset. While none of the models 
suggest it...some patchy valley fog could develop as was the case 
this morning. For now...left out this mention in the tafs as it may 
have little impact on terminals. 


Outlook.../Saturday night through Wednesday/... 
VFR conditions will continue through Monday before possible 
restrictions in showers return Tuesday with an approaching warm 
front. 


&& 


Pbz watches/warnings/advisories... 
Maryland...frost advisory from 2 am to 8 am EDT Sunday for mdz001. 
Ohio...frost advisory from 2 am to 8 am EDT Sunday for ohz040-041-050. 
PA...freeze watch from late Sunday night through Monday morning for 
paz007>009-015-016. 
Freeze warning from 2 am to 8 am EDT Sunday for paz007>009-015- 
016. 
Frost advisory from 2 am to 8 am EDT Sunday for paz013-014- 
020>023-029-031-073>076. 
WV...frost advisory from 2 am to 8 am EDT Sunday for wvz001>004-012- 
021>023-041. 


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34/kramar