Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1041 am EDT Wednesday Jul 30 2014
low pressure in eastern Canada will bring temperatures a little
below normal through tomorrow night with chances each day for an
afternoon shower or thunderstorm. A return to more normal Summer
temperatures is expected Friday and into this weekend... with a
continued chance for an afternoon and evening shower or
Near term /until 8 PM this evening/...
as of 1041 am EDT Wednesday...inherited forecast in pretty good
shape this morning though needed an update to probability of precipitation/sky/wx to
account for latest trends. Generally looking at a quiet day across
most of the north country as an upper trough/low over eastern
Canada is in control of our weather for the near and short term
periods. Still looking at the potential for some isolated showers
and maybe a T-storm this afternoon across northern New York as
weak shortwave energy scoots along the international border over the St.
Lawrence River...though latest rap/hrrr/btv6 are highlighting
weaker energy and thus less activity. Have lowered probability of precipitation a
little...but maintain chance across northern New York. Less
chances across Vermont.
Short term /8 PM this evening through Friday/...
as of 442 PM EDT Tuesday...
Second short wave moves across the region tonight so even with
waning surface based instability waning can't rule out a shower
or thunderstorm especially this evening as temperatures continue to cool
aloft. A partly cloudy night for most of US with low temperatures mainly
in the 50s.
On Thursday...finally the strongest wave with fairly strong qg
forcing from vorticity advection and better instability from cold
temperatures aloft (-20c at kmss) by 18z Thursday.
Timing of this feature will play a large role in the amount of
instability we see with models showing an early arrival which
will limit convective potential. European model (ecmwf) continues to show more
instability (up to 1500 j/kg) than most of the other models, but
all show some. So showers are likely first in New York in the morning
and region wide through midday with best chance of thunder mainly
in Vermont through the afternoon. With cold pool aloft and lower
freezing levels (~8-9k ft) could see some small hail with any
stronger updrafts which do develop...but will leave out for now.
850 temperatures 8-11c should give US high temperatures in the 70s.
Thursday night short wave is exiting so chances of precipitation
diminish with partly cloudy skies and temperatures falling back into the
50s. Some patchy fog possible again.
On Friday the upper trough is weakening and lifting north leaving
US in a broad SW flow aloft with 850 temperatures up around 12-13c
should give US a partly sunny day ' with highs in the 70s to
around 80 right about normal for the August 1. Some small chance
of a shower or thunderstorm but less than Thursday as instability
Long term /Friday night through Tuesday/...
as of 356 am EDT Wednesday...large scale features indicate a highly
amplified pattern will continue across the Continental U.S. With middle/upper
level trough across the Great Lakes sandwiched between strong
ridges over the western Atlantic and the inter-mountain west. There
are indications though that this pattern will relax a bit later in
the period with flow becoming more zonal...at least temporarily.
With the upper trough over the Great Lakes for much of the
period...expect a fairly active pattern across the northeast with
rather moist southwest flow and several embedded vorts in the
flow aloft bringing chance of showers and perhaps a few storms to
the region. Probabilities for rain look to be greatest during
afternoon hours each day...associated with time of maximum heating.
Precipitation chances overnight/early morning will be
lowest...with generally no higher than slight chance indicated.
Temperature profiles fairly uniform through the period with 850 mb
temperatures mostly between 11-13c. With partial sun...this supports
highs in the middle 70s to lower 80s. These readings close to seasonal
norms. Min temperatures expected to range from the 50s in the mountains
to lower and middle 60s in the valleys.
Aviation /15z Wednesday through Sunday/...
through 12z Thursday...fog with vlifr conditions at mpv till about
13z. Otherwise...mostly VFR conditions for the rest of the period
at all taf sites. Expect a broken deck of middle clouds this
morning...then scattered-broken cumulus clouds this afternoon/evening
along with chance shower or thunderstorm...with brief MVFR
conditions possible at mss/slk after 18z. Have included mention
vcsh to account for this. Fog chances tonight limited due expected
cloud cover. Have indicated MVFR conditions at mpv after 06z with
VFR at rest of sites. Winds south to southwest 10 kts or less
today...then light southerly tonight.
Outlook 12z Thursday through Sunday...
12z Thursday - 00z Friday...scattered showers and thunderstorms with
localized MVFR/IFR conditions in the heavier showers/storms.
00z Friday Onward...mainly VFR although brief periods of MVFR possible
in scattered afternoon showers or thunderstorm each day.