Area forecast discussion
National Weather Service State College PA
1129 am EDT Sat may 18 2013
Synopsis...
A wavy frontal boundary extending from the upper Midwest through
the Ohio Valley and across the central Appalachians into southern
Middle-Atlantic States will slowly return northward as a warm front
through Monday. The warm front will then stall out across upstate
New York and New England before sinking back to the south and
oscillating over Pennsylvania into the middle of next week. The
front should finally push south of the area by late next week or
early in the weekend...as a large Canadian high pressure system
drops southeast into the Great Lakes region. Overall expect a
prolonged stretch of unsettled weather over the next several days.
&&
Near term /until 6 PM this evening/...
Another minor update.
Radar showing showers moving out of north central PA.
MDT...cxy...and bfd had a few minutes of rain earlier.
Another area formed across the southeast.
Still a decent area of mainly clear skies across the SW
part of PA.
Clouds thinning across Michigan and upstream points...but left
slight chance in...as a few showers could form just about
anywhere. Did take thunder out of the SW. Did not want
to go dry there...given higher dewpoints and higher probability of precipitation
to the the SW.
Earlier discussion below.
Middle/high clouds cover most of the area this morning. Filling upper
low sliding well to our south but slowing as it does so. Weak surface
ridge over the northeastern states will also move to the east.
Light east wind will veer a bit and allow more moisture into the
region. So far...no sign of any clouds less than 6kft off to our
S/E. Previous forecasts of an increase in lower clouds is right
on...finding support in all models in the next 6-12 hours. But the
schedule may need to be hurried up a few hours if current timing
from mesoscale models is right. This thickening/lowering of the clouds
will have a detrimental effect on the temperatures in the southern mts as the
lower clouds will arrive/develop there first later today. Current
temperatures m50s-l60s in that area...and it will be tough to add much
more than 10-12f onto those numbers today. Have kept maximum temperature at
70 or just below for places S of State College. Will mention just
a sprinkle for the next few hours in the southeast and northwest...but then dry
until this afternoon. Sun still possible in the northwestern mts and
elevations/heating will make diurnal cumulus and perhaps lower
stability enough to pop a shower or two. Current 30 dewpoints will
be the knock on that possibility. 20-30 probability of precipitation will hold there.
&&
Short term /6 PM this evening through Monday night/...
Seems like a no-brainer to forecast thick lower clouds tonight over
much of the area...and the upslope flow will create patchy light
rain or drizzle over much of the area through the night.
However...amounts should be light enough that a 100 pop seems over
done. Will go with 50-60 probability of precipitation in the upslope areas and central
mts. The northwest will stay the driest and see the least cloud coverage.
Surface/low level pattern changes little through Sunday evening.
Persistence forecast should be solid. But will taper probability of precipitation a bit each
period due to uncertainty on placement of the patchy rain/showers.
Still expecting that the bulk of any decent rain in the short term
period will remain to the south along the pesky stationary front.
With all the cloud cover...temperatures will have little diurnal range.
Some drying is prognosticated Sun night or Monday and could lead to lower
stability Monday - as the /warm/ front attempts to push through
the local area. Thus...the chance of thunder makes it into the forecast
then.
&&
Long term /Tuesday through Friday/...
The last two cycles of global guidance continues to depict a
highly amplified 500mb pattern holding firm through the medium
range period. A compressed wavelength between Pacific northwest closed
low/High Plains ridge/upper MS valley closed low/trough and southeastern U.S.
Ridge will eventually Widen and evolve to a western trough/plains
ridge/eastern trough configuration /essentially a Continental U.S. Omega block/
by the end of the period. In general...the oprn models and ens means
show reasonably good agreement on the large scale synoptic features
with the usual timing/placement diffs related to surface fronts and
quantitative precipitation forecast - which is to be expected at this range.
In terms of sensible weather highlights...the overall pattern will
be a rather unsettled and potentially very wet one with daily
opportunities for convective precipitation. With precipitable water values
above normal through the entire period...went above climatology probability of precipitation
using an even blend of GFS/ec based MOS data. Temperatures in the
first half of the period /days 4-5 or Tue-Wed/ should average several
degrees above late-may climate normals. This warm spell should be
followed by a gradual downward trend in maximum/min for days 6 and 7
threshold-Friday (and likely into day 8/sat) with a cold front expected to
move through the region sometime late next week.
&&
Aviation /16z Saturday through Wednesday/...
5-18/16z...
VFR flying will continue this afternoon across most of the area...
with broken-overcast Alto cumulus bases around 7-10kft above ground level.
However...just starting to see lower clouds working northward from
Maryland and Virginia...into Bedford County...south of aoo. Strong sun angle...
similar to middle July...may try to slow down northward edge of this
area of clouds...but expect the the low-level flow to continue veer
to the southeast this afternoon and direct increasingly moist/maritime air
into the region. This will result in lowering ceilings this evening with
widespread MVFR to IFR conds expeceted tonight through Monday. Confidence
is above average.
A stationary frontal boundary will lift slowly northward across
the airspace by Tuesday...which should allow for some marginal
improvement in local flying conds. A rather unsettled and potentially
wet pattern is expected during the middle to second half of next
week...with daily chance/S for convective precipitation and associated restrictions.
Outlook...
Sun-Mon...MVFR-IFR ceilings.
Tue-Wed...VFR-MVFR with scattered PM thunderstorm impacts.
&&
Ctp watches/warnings/advisories...
none.
&&
$$
Synopsis...dangelo/steinbugl
near term...dangelo/Martin
short term...dangelo
long term...steinbugl
aviation...Martin/steinbugl
