Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Albany New York
435 am EDT Thursday Jul 31 2014
a disturbance rotating around an upper level low over
southern Canada will set off some showers and thunderstorms
today...some of which may be strong to severe. The threat for
showers and thunderstorms will continue into the next few days due
to the nearby upper level low and a stalled frontal boundary off the
eastern Seaboard...with increasingly warmer and more humid
conditions returning to the region through the upcoming weekend.
Near term /until 6 PM this evening/...
as of 435 am EDT...a closed off upper level low is situated near
James Bay over eastern Ontario. This upper level low is basically
expected to sit and spin through the day today...with a vorticity
maximum swinging around the base of the low towards the northeastern
US. Showers and thunderstorms are expected to develop through the
day today during daytime heating thanks to the lift from this
disturbance and rapidly move from west to east across the area.
In additon to 500 hpa temperatures being very cold for late July /around
-16 degrees c/...there will be decent middle level lapse rates of 6
to 6.5 degrees c per km...and 0-6 km bulk shear of around 40 kts.
Even though dew point will generally be in the 50s...enough instability
will be present...with cape values 500-1500 j per kg. Our local
hireswrf and the 3km hrrr show cellular storms moving quickly
across the area between the late morning and early evening hours.
With the cool temperatures aloft...large hail around 1 inch in diameter
will be the biggest threat with any storm...although some bowing
segments could allow for gusty winds within the strongest storms as
well. The higher threat may be across northern parts of the area
/closer towards the upper low/ but we can/T rule out a strong to
severe storm across the entire area. We will include enhanced
wording in our grids...and continue to monitor radar trends
through the day.
Maximum temperatures will continue to below normal for late July...thanks to
the cool temperatures aloft and proximity of the upper level low...as
well as the clouds and possible rainfall. Maximum temperatures look to mainly
be in the 70s.
Short term /6 PM this evening through Saturday night/...
the shortwave responsible for the showers/thunderstorms will move
northeast of the area tonight...ending the threat for precipitation...as
the whole upper level low wobbles towards western Quebec. As a
result...mainly dry weather is expected tonight...with cool lows
in the 40s and 50s.
During the day Friday...the upper level low will start to weaken
and move northeast across Quebec. However...a large scale trough
will continue to be situated over the area...as a trough axis digs
across the Great Lakes/Ohio Valley...and ridging strenghtens over the
western Atlantic. This will allow for a broad S-SW flow over our
area...which will start to return moisture to the area.
Meanwhile...this set up will help establish a stationary boundary
right along the eastern Seaboard...which will help focus some
showers and thunderstorms for Friday afternoon into Friday night. These will
mainly affect southern and eastern parts of the area. Maximum temperatures on
Friday look to reach the middle 70s to low 80s...and mins will mainly
be in the middle 50s t0 low 60s.
The pattern will be rather stagnant for Sat/Sat night....with a
trough axis just upstream over the Ohio Valley...and a stationary
boundary right off the coast. Showers and thunderstorms will
continue to be possible...especially during the diurnally favored afternoon
and evening hours. It will start to be noticeably more humid with
dewpoints returning into the 60s for most areas. Temperatures will be
similar to Friday...with highs near 80 and lows generally in the
middle 50s to middle 60s.
Long term /Sunday through Wednesday/...
guidance is in good agreement that the amplified longwave pattern
will continue to weaken as we head into next week...however the
trough will linger over the region. At the surface...the nearly
stationary boundary along the East Coast will gradually dissipate as
we head into next week. In the meantime...northern stream energy
moving across eastern Canada will help push as cold frontal boundary
across the northeast Monday and Monday night. There are some
differences with the strengthen and timing but overall our weather
will remain unsettled as we close out the weekend and head into next
week. Precipitable water values and dew points will rise ahead of
the approaching cold front so some heavy downpours are expected.
With passage of the cold front a less humid airmass will be ushered
back into the region with weak high pressure building in at the
surface for middle week.
Temperatures to start out August are anticipated to seasonably warm
with highs generally in the middle 70s to lower 80s and lows in the middle
50s to lower 60s. The coolest day should be Sunday due to extensive
Aviation /08z Thursday through Monday/...
a potent short wave is rotating about the upper low over eastern
Canada and will move over the region today along with its associated
cold pool extending southward into the local area. A round of
showers and thunderstorms will accompany these features as they
approach later this morning and move over the region this afternoon.
Have addressed threat for convection with tempo groups generally 16z
to 20z in the kgfl...kalb and kpsf tafs while down in kpou have used
vcsh where likelihood for convection is less.
Overall VFR conditions will dominate through the taf period...the
exceptions will be the possibility for MVFR fog at kpsf early this
morning and MVFR conditions will storms. IFR will be possible with
convection however it should be brief and has not been included in
tafs. Threat for convection will end by late this afternoon as short
wave moves off our northeast.
Light to calm winds overnight with a south to southwest flow
developing Thursday at 5 to 10 knots. The winds will diminish
during the evening.
Friday night: moderate operational impact. Chance of rain showers...tsra.
Saturday: moderate operational impact. Chance of rain showers...tsra.
Saturday night: moderate operational impact. Chance of rain showers.
Sunday: moderate operational impact. Chance of rain showers...tsra.
Sunday night: moderate operational impact. Chance of rain showers.
Monday: moderate operational impact. Chance of rain showers...tsra.
Monday night: no operational impact. No sig weather.
Tuesday: moderate operational impact. Chance of rain showers...tsra.
showers and thunderstorms are possible today...with the greatest
threat between the late morning hours and early evening hours.
This will bring a wetting rainfall to some locations...especially
northern parts of the area. Relative humidity values will only fall to around 50
percent this afternoon due to the clouds and possible precipitation with
S-SW winds of 5-10 miles per hour.
Relative humidity values will return to nearly 100 percent tonight with light to
calm winds and dew formation. Relative humidity values will only fall to around
50 percent on Friday afternoon...with some more rain showers or
thunderstorms possible...mainly for southern parts of the area.
some showers and thunderstorms are possible today thanks to an
upper level low situated north of the area. While showers or
thunderstorms may produce a brief period of heavy
rainfall...flooding is not anticipated...as these storms should be
quick moving...and overall moisture content is not as high as some
previous thunderstorm events from earlier this Summer. These storms may be
enough to cause ome ponding on roadways...but no widespread flood
concerns are anticipated.
However...warmer and more humid conditions will be gradually returning
over the next few days. With a contineud threat for showers and
thunderstorms...locally heavy downpours could occur...and minor
flooding of poor drainage and urban araes will be possible if
thunderstorms repeatedly pass over the same locations...especially by Sat
and Sunday...when precipitable water values will be as high as 1.90 inches over
far southern parts of the area.
For details on specific area rivers and lakes...including observed
and forecast river stages and lake elevations...please visit the
advanced hydrologic prediction service /ahps/ graphs on our website.