Albany, NY WFO Forecast Discussion

000
FXUS61 KALY 092355
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
755 PM EDT Thu Jul 9 2020

.SYNOPSIS...
It will remain muggy into tonight with area of low clouds and
fog. Fairly warm and sticky conditions will continue for
Friday and into the weekend. Tropical low pressure moving up
the coast from the mid Atlantic States will bring a period of
rain showers to the region for late Friday into Saturday
morning, some of which may contain heavy downpours. Warm, humid
and unsettled weather will continue for the remainder of the
weekend into early next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 745 PM EDT...Isolated convection across the Catskills,
Berkshires and southern Greens are dissipating. Rather efficient
rainfall producers with minimal steering currents aloft and a
very warm lower troposphere. Impressive max heat index values
were observed (see PNS for details) with a few 100 degree
readings. As temperatures are slowly receding, this too will
impact the heat index values as we will expire the advisory at 8
pm EDT. Overnight, as the past couple of nights, low
stratus/fog formation is expected due to moist low levels and
light winds. So main update was to remove heat headlines,
refresh hourly trends per observations, PoP/Wx grids for the
remaining isolate convection the next couple of hours, and sky
coverage per GOES imagery trends.

Prev Disc...By this evening, any showers or thunderstorms will
dissipate with the loss of daytime heating. The surface low
pressure will only be slowly lifting northwards towards offshore
the Virgina Capes and Delmarva, although upper level ridging
will continue to hold across our area. As a result, it should
stay rain-free across our area. With the muggy air mass in
place, some low stratus or fog could develop again overnight.
Lows will generally be in the mid 60s to low 70s across the
area.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Developing tropical low offshore the mid Atlantic coast will be
continuing to lift northward on Friday as the upper level
ridging exits off to the east. Although the morning will start
off dry, clouds will be increasing from the south. PWAT values
will be rapidly increasing through the day, exceeding 2 inches
for the entire area.

Although the timing is still some uncertain, periods of showers
will be lifting up from the north and should be reaching into
our southern zones by Friday afternoon. The combination of a high
freezing level, warm rain processes and high PWATs will result
in very efficient precip. Rainfall rates will have the potential
to exceed an inch per hour within the heaviest showers. Have
included a slight chance for thunder as well, although thunder
may be limited due the skinny CAPE profile in place. Despite a
lack of widespread thunder, locally heavy downpours will be
possible.

As low pressure continues to lift northward, rain will be
lifting south to north across our entire area. The period of
heaviest rain across our CWA looks to be on Friday night. With
the southeast flow, high terrain areas (such as the Catskills,
Berkshires and Litchfield Hills) may see some enhanced precip
due to upslope flow. With the potential for high rainfall rates,
have gone with a Flash Flood Watch for southeastern parts of the
area. However, this may need to be expanded northward in time. A
widespread one to two inches of rain looks to fall across the
region, although locally higher totals (3 to 4 inches) are
certainly possible.

In addition, there may be a localized threat for an isolated
tornado or severe wind gusts on the northeast corner of the
storm as it lifts northeast due to the strong winds aloft and
high amounts of low-level shear. This is still very uncertain,
but may need to be watched closely, as the surface low lifts
northward close to our area on Friday night.

By Saturday morning, the main storm system will be departing off
the north or northeast. Some clearing should be occurring on
Saturday morning, however, there will be a threat for some
additional showers and thunderstorms by afternoon as an upper
level shortwave approaches from the west. With abundant
instability expected to be in place due to the warm and muggy
air mass still around, there could be some strong to severe
storms during the afternoon hours. 0-6 km bulk shear looks to be
about 20 to 30 kts, so there could be enough shear for some
organization of storms. Threat for storms should diminish by the
late evening hours. Can`t rule out a few lingering showers
Saturday night, but main threat should be done as the shortwave
starts to depart off to the east.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Overall low confidence forecast into the long term as we will watch
the departing tropical system to the north, then a series of short
waves diving southward within the northwest to west flow through the
mid-week period.

Global models, along with dprog/dt of the guidance, the ECMWF
Fujiwara appears to be an outlier for end of the weekend with the
GFS/GFS-Para run/GGEM and the NAM appear to be a little drier with
subsidence behind the departing tropical system.  For now, we will
cut back PoPs a bit with a very warm and humid air mass across the
region where isolated convection is possible.  Now, the upstream
short wave moving through the Great Lakes region and Ohio Valley
appears to approach after 00Z Monday.


Sunday night into Monday, timing of the aforementioned upstream wave
approaches overnight, likely after 06Z Mon, then transverses the
region on Monday.  PWAT anomalies per the GEFS are not out of
tolerance but overall shear is favorable for organized convection.
So we will place increasing PoPs overnight Sunday leading into
likely PoPS on Monday.

PoPs should decrease a bit Monday night then next upstream wave and
another surge of higher theta-e air is forecast to arrive into the
mid-week period.  This would keep the weather unsettled with
additional chances of showers and thunderstorms.

Regardless, warm and humid conditions with dewpoints likely well
into the 60s with daytime highs into the 80s for valley
locations.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
VFR conditions with FEW-SCT clouds expected through the rest of
the evening hours at the TAF sites.

Once again, fog and/or low stratus clouds likely to develop,
especially at KGFL/KPSF with IFR conditions. A little higher
confidence per latest forecast sounding profiles in IFR
conditions occurring at KALB/KPOU so we will include a TEMPO
groups at this time.

Any fog should dissipate by around 12Z-13Z Friday, but low stratus
clouds with MVFR cigs will likely linger at KPOU/KPSF as moist
southeast flow develops ahead of a coastal low approaching from the
south. Scattered showers will be possible at KPOU starting around
16Z. PROB30 groups were introduced at all TAF sites from 16-18Z
through 00Z/Sat.

Winds will become variable less than 5 kt tonight. Winds from
12Z-18Z Friday will be southeast around 5-6 kt. We will watch
for increasing LLWS potential at KPOU for later Friday
afternoon.

Outlook...

Friday Night: High Operational Impact. Definite SHRA...TSRA.
Saturday: High Operational Impact. Likely SHRA...TSRA.
Saturday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Sunday: Low Operational Impact. Slight Chance of SHRA...TSRA.
Sunday Night: Low Operational Impact. Slight Chance of SHRA...TSRA.
Monday: High Operational Impact. Likely SHRA...TSRA.
Monday Night: Low Operational Impact. Slight Chance of SHRA...TSRA.
Tuesday: Moderate Operational Impact. Chance of SHRA...TSRA.

&&

.FIRE WEATHER...
Warm and humid conditions will continue to be in place for
Friday through the weekend. RH values will generally be above
50 percent each day, with a recovery to near 100 percent each
night with dew and fog formation. There should be a pretty good
chance for a widespread wetting rainfall Friday night into
Saturday morning for most areas. South to southeast winds will
mainly be 5 to 10 mph through the weekend.

&&

.HYDROLOGY...
A moisture-rich coastal system will move up the Eastern
Seaboard Friday into Saturday. Due to a strong south-
southeasterly fetch, guidance indicates it will direct a plume
of moisture from the tropics towards the Northeast. With
precipitable water values in excess of two inches, 850mb
moisture flux values range +2 to +3 standard deviations.
Therefore, this system will be capable of producing moderate to
locally heavy rainfall. While the National Hurricane Center is
also closely monitoring this system, its ability to produce
heavy rainfall will be maintained whether or not it becomes a
more organized tropical system or is named.

Model guidance still has some differences regarding the timing
and track of the surface low and where the heaviest axis of rain
will be. There is starting to be some consensus that the storm
will track close to our area, so a widespread 1 to 2 inches of
rain is becoming more likely, with localized totals of 3 to 4
inches possible. MMEFS still does not indicate any flooding on
area rivers due to antecedent dry conditions and low flows in
place. However, shorter-fused urban/small stream flooding or
flash flooding still cannot be ruled out.

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.

&&

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...Flash Flood Watch from Friday afternoon through Saturday
     morning for CTZ001-013.
NY...Flash Flood Watch from Friday afternoon through Saturday
     morning for NYZ058>061-063>066.
MA...Flash Flood Watch from Friday afternoon through Saturday
     morning for MAZ001-025.
VT...None.

&&

$$
SYNOPSIS...Frugis/BGM
NEAR TERM...Frugis/BGM
SHORT TERM...Frugis
LONG TERM...BGM
AVIATION...BGM/JPV
FIRE WEATHER...Frugis
HYDROLOGY...Frugis/Speciale

NWS ALY Office Area Forecast Discussion