Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1029 am EDT Sat Oct 25 2014
weak high pressure will build across the area today
with some partial sunshine and milder temperatures. Upper level
energy will then drop southeast into the region from Canada tonight
into Sunday with a renewed threat of showers and higher Summit snow
showers. Precipitation tapers off by Sunday night with high pressure
returning by Monday and Tuesday of next week with generally dry
weather and moderating temperatures.
Near term /until 6 PM this evening/...
as of 1019 am EDT Saturday...going forecast in good shape. Only
minor adjustments with latest update to reflect latest conditions
and trends. Clouds overspreading northern New York at this time...and
will advance east across Vermont this afternoon. Shower threat
holds off in northern New York till middle PM and in Vermont till late
PM/evening with arrival of strengthening shortwave from the
northern Great Lakes. Still looking at maximum temperatures in the middle 50s to
forecast remains on track for today as default shortwave ridging
skirts quickly through and east of the region. Thus at least some
partial sunshine through the morning and early afternoon hours
under light south winds. 925 mb thermal profiles at 18 UTC average
7 to 10c or so...so adding the typical 7-8c for lower elevations
during the autumnal (or vernal) seasonal period supports highs
ranging from 55 to 60 across our area today. By later this
afternoon models in good agreement showing rather vigorous
northern stream shortwave energy dropping quickly southeast toward
the area with fairly impressive positive vorticity advection and height falls aloft. Thus
running idea of increasing clouds and chances of showers still
appears on track by later this afternoon across our northern New York
counties...and toward early evening across central/northern Vermont. Threat
of showers lower across southern Vermont.
Short term /6 PM this evening through Monday/...
as of 330 am EDT Saturday...by tonight scattered/numerous showers to
continue as shortwave and upper energy drops into the region...especially
across the central/north. As flow trends west/northwesterly aloft
later tonight...freezing levels will drop to around 3000 feet or so
with precipitation mixing with or changing to snow at The Summit level or
slightly below. Lows from the upper 30s to middle 40s below the 2000
feet level. Being of Continental origin...system will have only
modest moisture to work with however so not looking at anything
By Sunday into Sunday evening we remain under the influence of the
upper shortwave trough with cyclonic west to northwesterly flow
aloft and plenty of clouds. Flow will become blocked over time such
that shower coverage will become increasingly confined to the
northern mountains where some light addl snowfall will remain possible
above 2500 feet or so. High temperatures about 7 to 12 degrees
cooler than today...or generally in the middle 40s to lower 50s. Lows
Sunday night in the 30s to around 40.
By Monday still good consistency among this morning's global
solutions in showing moderately amplified longwave ridging to begin
pushing east from the central states with rising heights aloft and
diminishing northwesterly surface flow. Still some lingering/vrb
clouds...especially northeastern half of the forecast area where a brief
sprinkle will remain possible during the first half the day across
the higher terrain. Dry elsewhere. Highs a blend of available guidance
supporting values from the upper 40s to middle 50s...or within 2 degree of
late October seasonal norms.
Long term /Monday night through Friday/...
as of 403 am EDT Saturday...overall idea for the extended period
remains in good shape from previous forecast thinking with the
latest GFS and European model (ecmwf) coming into good agreement in regards to the
overall synoptic pattern.
Upper ridge continues to build across the northeast Monday night
into Tuesday while high pressure over the southeast shifts offshore
and low pressure develops upstream over the western Great Lakes.
Pressure gradient between these features increases southerly flow
across the northeast with 1000-500mb thicknesses rising to around
565dm Tuesday afternoon. 850mb temperatures rise to near +11c supporting
highs well above normal in the middle 50s to middle 60s under partly sunny
skies. As the surface low shifts northward from the Great Lakes to
east of James Bay Tuesday night into Wednesday morning...it
intensifies and a thermally strong but moisture lacking cold front
tracks through the region. Uncertainty still exists with the exact
timing of the boundary with European model (ecmwf) still a little bit slower than
the GFS. Based on the amplification of the ridge ahead of the
front believe the European model (ecmwf) is on the right path so have leaned in
that directions offering a frontal passage during the early morning hours of
Wednesday with light quantitative precipitation forecast amounts and temperatures falling sharply through
the day under strong cold air advection.
Behind the front for Thursday and Friday conditions are generally
dry with zonal to southwesterly flow developing aloft as another
upper trough digs into the Great Lakes. We'll return to more fall-
like temperatures with the 540dm thickness line well south of the btv
County Warning Area and daytime highs only in the 40s and 50s and lows in the 20s
and 30s. There's some uncertainty on precipitation probs for Halloween at
this time as the GFS and European model (ecmwf) handle said trough differently.
Have trended dry for now...but the jury is still out.
Aviation /14z Saturday through Wednesday/...
through 12z Sunday...generally clear skies with some scattered cirrus
this morning will trend towards a broken-overcast VFR deck this afternoon
as a cold front swings into the region. Kslk is currently under a
dense LIFR stratus deck...which will slowly erode through the next
2 hours...lifting into a VFR deck. A short 1-3hr period of
showers accompanies the front as it moves west to east across the
County Warning Area...but expect visibility to remain VFR maybe briefly MVFR. Ceilings will
lower area-wide to MVFR during precipitation and behind the front with
winds shifting from the south to west- southwest after 00z.
Outlook 12z Sunday through Wednesday...
12z Sunday - 12z Monday...a mix of MVFR and VFR associated with a
second round of valley rain showers and mountain snow showers
behind an exiting front on northwest flow.
12z Monday - 06z Wednesday...VFR under building high pressure.
06z Wednesday - 00z Thursday...VFR with some areas of MVFR in
rain showers as a cold front moves through the region.