000 
fxus61 kaly 211733 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
133 PM EDT Sat Jul 21 2018 


Synopsis... 
fair and dry weather for the rest of the afternoon with 
seasonable temperatures with high pressure near the region. A low 
pressure system developing to our south is expected to move 
northward, bringing periods of rain and isolated thunderstorms 
tomorrow. In addition, a warmer and more humid airmass will move 
into the region allowing for more rainfall and thunderstorms 
possible into the middle of the week. 


&& 


Near term /until 6 PM this evening/... 
as of 133 PM EDT...a nice mid to late July afternoon with some 
mid and high clouds drifting in from the south and west 
associated with low pressure lifting north and east from the ern 
NC Carolina coast tied to a cutoff low over the lower Great 
Lakes region. The cutoff is embedded in a negatively tilted long 
wave trough which will allow the coastal wave to move quickly 
northeast with the sfc high retreating slowly off the Atlantic 
coast some. 


Clouds will increase the rest of the afternoon, but mostly 
sunny/sunny conditions should prevail into the mid afternoon. 
We have adjusted hourly temperatures to better fit rising 
temperatures with highs still expected to be in mainly in the 
mid 70s to lower 80s. 


The 12z kaly sounding was still very dry, as indicated by the 
T/dew point profile, but also the precipitable water of 0.58". That will be changing 
over the next 12-24 hrs. Onset timing of the 3-km NAM/hrrr is 
favored at this time, which will allow the window for deep 
moisture and coastal storm to track northward. 


More on that in the short term below... 


&& 


Short term /6 PM this evening through Monday night/... 
as seen in the GOES 16 data, coastal wave was developing 
off the North Carolina coastline as pressure falls were underway 
per the msas analysis the past few hours. Meanwhile, upstream 
mid level jet near 70kts and convection across eastern Kentucky/Tennessee 
was continuing as trough continues to dig southeastward from the 
central Great Lakes. All of these pieces in the atmosphere will 
make for a complex impact across our local region. Trends in the 
hi-res runs suggest this coastal wave will track along the 
coastline and inland with an increase in forward momentum. This 
would limit the rainfall window across the region as rain will 
overspread the area from south to north and most of it ending 
south of i90 by 12z Sunday and quickly ending across the north 
toward 15z Sunday. The other aspect to ascertain will be the 
winds as h850 wind anomalies from the southeast direction will 
be quite high with values near 6 Standard deviations in both the 
u-v components. Our portions of the Catskills, Taconics, 
Northwest Hills of CT, Berks and southern greens are usually the 
most susceptible to higher gusts as MOS is finally catching up 
with this possibility. As this time, no headlines as current 
soundings suggest a stable layer but will continue to monitor 
closely, especially if deeper convection were to be realized. 


There will likely be a period of minimal activity later Sunday 
morning into the afternoon hours as mid level dry slot quickly 
advects across the region. Southerly winds up the Hudson could 
become quite gusty if we achieve additional sunshine as mixing 
layer heights and momentum equations point toward 30kts. 


Then the next surge of moisture, which will be persistent 
through the short term, arrives late Sunday into Sunday night. 
As precipitable waters  climb toward 2 inches and the Atlantic high building 
and retrograding through the short term, periods of showers and 
thunderstorms are the result. Period of heavy rainfall is 
possible later Monday into Monday night as a region of 
confluence within the high precipitable waters  due to deep tropical connection 
could result in training of rainfall. Currently due to our dry 
antecedent conditions and the coastal storm likely resulting in 
quantitative precipitation forecast values an inch or less (highest in the catskills), not 
expecting widespread issues at this time. 


Temperatures will be rather mild and muggy as 70s and 80s for 
highs and overnight lows in the 60s to lower 70s as dewpoints 
will be close to those overnight temperatures. 


&& 


Long term /Tuesday through Friday/... 
an amplified upper level pattern will remain in place over the 
eastern Continental U.S. For much of the long term period, which will allow for 
a continuous moist southerly flow across our region. 


Our region will be sandwiched between a strong upper level ridge off 
the eastern Seaboard and an upper level trough over the Great Lakes 
and the Ohio and Tennessee Valley regions. Initially, there will be 
a closed low over the deep south that will weaken on Tuesday. 
However, the trough remaining in place will be reinforced through 
the week by another large upper level low dropping out of central 
Canada. 


For Tuesday, the upper level ridge will try to build westward into 
New England. This may help to limit the coverage and extent of 
diurnally forced showers and thunderstorms. Although it still 
appears that showers and thunderstorms will form, they may be more 
likely for the western half of the area. By later in the week, the 
upper level trough will shift eastward and the ridge will be moving 
away. This may allow for the better chance for more widespread 
showers and thunderstorms for Wednesday and especially Thursday. 


The strong southerly flow at low to mid levels will allow for precipitable water 
values to build to near two inches, which is 1 to 3 Standard above 
normal. As a result, locally heavy downpours will be a threat each 
day and the persistent precipitation and chance for training storms 
will enhance the threat for flooding, especially by later in the 
week. Some locations may wind up seeing at least several inches of 
rain this week. At this point, it's too early to pinpoint which 
areas will see the heaviest rainfall, but southern facing slopes of 
the high terrain may be at a higher risk due to the possibility of 
some upslope enhancing rainfall in those areas. It may take until 
the weekend to finally break this pattern, although there really 
isn't any sign of any large ridging returning to the region anytime 
soon. 


Temps each day should reach the upper 70s to mid 80s, as enough 
breaks of sun should occur in the morning or early afternoon to 
allow temps to warm up before convection allows for more clouds. It 
will remain muggy overnight with lows in the 60s. Dewpoints look to 
be well into the 60s, making for a rather uncomfortable week as 
well. 


&& 


Aviation /18z Saturday through Thursday/... 
early morning fog at kgfl/kpsf is in the process of dissipating 
and shouldn't be an issue by the start of the taf period (12z 
saturday). 


Upper level ridge is shifting offshore, but surface high pressure 
remains close enough to keep it rain-free through the day today. Infrared 
satellite imagery shows bands of high clouds are moving across 
southern parts of the area and these clouds will continue to 
increase and expand across the entire area through the day, with 
continued VFR conditions. South to southeast winds will be 5 to 10 
kts for all sites. 


By evening, rain will be moving up from south to north, as low. 
Pressure travels up the mid-Atlantic coast. Kpou could see a 
shower as early as 02z, but it probably won't be a steady rain until 
at least 04z. Rain will reach kpsf/kalb/kgfl by 03z-07z. Within the 
steady rain, flying conditions will likely lower to MVFR and IFR for 
the rest of tonight as well, as some locally heavy downpours will be 
possible. Winds will switch to the east-NE and start to become gusty, 
especially at kpsf/kpou, where wind gusts of 20 knots are 
possible. 


Outlook... 


Sunday night: high operational impact. Numerous rain showers...tsra. 
Monday: high operational impact. Numerous rain showers...tsra. 
Monday night: moderate operational impact. Scattered rain showers...tsra. 
Tuesday: moderate operational impact. Chance of rain showers...tsra. 
Tuesday night: moderate operational impact. Chance of rain showers...tsra. 
Wednesday: moderate operational impact. Likely rain showers...tsra. 
Wednesday night: moderate operational impact. Chance of rain showers...tsra. 
Thursday: high operational impact. Likely rain showers...tsra. 


&& 


Fire weather... 
dry weather will persist through today. Unsettled conditions 
return tonight and into the second half of the weekend as a 
coastal storm and frontal system impact the region. 


Relative humidity will fall to 30-50 percent this afternoon and recover to 
80-100 percent tonight, with periods of rain. 


Winds will be mainly from the southeasterly direction at 5-10 
mph today then become northeasterly into tonight with an 
increase in speeds. Higher magnitudes across the higher 
terrain. 


&& 


Hydrology... 
dry weather is expected through at least today. 


A wave of low pressure will develop across the southeast United 
States and track northward tonight. This is expected to spread 
a period of rain with perhaps a thunderstorm tonight into 
Sunday. Forecast rainfall amounts up to an inch are expected 
with a few isolated higher amounts where deeper convection is 
possible. These values should have minimal impact to area river 
and streams as levels are quite low and our recent dry 
conditions as noted in the latest drought monitor of d0-d1 
levels. 


Then a slow moving frontal system approaching from the west, 
along with a several waves of low pressure tracking northward 
within a very moist airmass in place, could lead to frequent 
showers and thunderstorms, some with locally heavy downpours for 
Sunday through at least the middle of next week. Potential 
exists for training elements that would result in water level 
rises. Stay tuned for further updates through the weekend. 


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...none. 
New York...none. 
Massachusetts...none. 
Vermont...none. 


&& 


$$ 
Synopsis...bgm/wasula 
near term...iaa/bgm/wasula 



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