Area Forecast Discussion


853 
FXUS61 KALY 220539
AFDALY
Area Forecast Discussion
National Weather Service Albany NY
1239 AM EST Thu Feb 22 2018
.SYNOPSIS...
The combination of snowmelt and recent rainfall may lead to 
some minor flooding over the higher terrain well north and west 
of the Capital District through tonight. Colder and more 
seasonable temperatures are expected on Thursday along with some
mixed precipitation in the form of snow, sleet and freezing 
rain. More unsettled weather is expected Friday and during the 
second half of the weekend.
&&
.NEAR TERM /THROUGH TODAY/...
Winter Weather Advisory from 4 AM until 6 PM Thursday for the 
eastern Catskills, Schoharie Valley and the Helderbergs.
As of 1230 AM EST... Rather quiet shortly after midnight with
ample cloud coverage per the Metars and enhanced nighttime
microphysics GOES-16 satellite channel. A northerly wind has
evolved down the Champlain with occasional gusts being observed
at KGFL. Otherwise, did increase cloud coverage in the grids and
to account for those northerly winds. Regional radar reveals a
few widely scattered showers across central and western NY and
into PA. Per the hires radar reflectivity forecasts from the
NAM3Km and HRRR/X suggest this will be on the leading edge of
the strengthening baroclinic zone and overall lift for the
slight chance PoPs into the Catskills, Schoharie Valley and
portions of NW CT toward sunrise with a rain/snow mixture
initially (could be a period of sleet). Remainder of the
forecast remains unchanged at this time.
Prev Disc...Surface high pressure over the Great Lakes will 
build eastward into the region, allowing the flow to turn out of
the north and continue to usher in colder air. Lows will be in 
the upper teens to mid 30s.
On Thursday some isentropic lift and overrunning precipitation 
is expected. Thermal profiles in the lower levels of the 
atmosphere will be critical for precipitation type. Expecting a 
mixture of snow, sleet and some freezing rain. It may be still 
warm enough for some rain in the mid Hudson Valley and 
Litchfield county. The freezing rain will be mainly confined to 
the advisory area and mainly occurring during the morning hours.
During the afternoon the primary precipitation type will be 
snow and some sleet. Highs on Thursday will be slightly above 
the overnight lows with highs ranging from the upper 20s to 
upper 30s. Temperatures may fall slightly during the afternoon. 
Snowfall amounts will range from 1 to 4 inches with up to a 
tenth of an inch of ice in the advisory area.
&&
.SHORT TERM /TONIGHT THROUGH 6 PM FRIDAY/...
A round of wintry mixed precipitation is possible Friday into Friday 
evening, mainly for areas above 1000 feet elevation. This would 
include light accumulations of sleet and freezing rain. 
Thursday night, high pressure over southern Canada will expand 
southward somewhat, resulting in the precipitation being shunted 
south of the forecast area. Cloud cover may clear somewhat for areas 
along and north of I-90, but will likely increase again toward 
sunrise Friday ahead of the next system. Some spotty very light snow 
or sleet is possible over the Catskills and Mid-Hudson Valley after 
06Z as a renewed bout of isentropic lift begins. 
Friday, the high shifts eastward over Nova Scotia while the low 
level jet magnitudes increase. This will result in a renewed round 
of moisture transport and isentropic lift, with precipitation 
becoming likely late morning into the afternoon. We'll start out the 
day cold with early morning temps in the teens and 20s, so some 
mixed precipitation is likely especially at the onset. The high is 
not in an ideal location to keep cold air locked in place, at least 
in the north/south valleys below 1000 feet, so currently do not 
expect much in the way of wintry accumulation there, as temps aloft 
and at the surface warm enough to support mainly rain as the p-type. 
Over the higher elevations of the Catskills and Adirondacks, thermal 
profiles support more in the way of a mixture of sleet and freezing 
rain for a good portion of the day. This will especially be true 
over the Adirondacks where a fairly deep snow pack still exists, and 
it has proven very difficult to scour out the cold air in similar 
circumstances. Still considerable uncertainty with respect to how 
much precipitation falls as sleet vs freezing rain, but additional 
winter weather headlines are a good possibility for the higher 
terrain above 1000 feet. As the temps aloft increase from west to 
east, the higher terrain of western New England may hold onto the 
colder temps longer, so perhaps more sleet or even light snow 
compared with freezing rain there.
Low-level winds veer Friday night spelling a gradual end to the 
isentropic lift, with weak high pressure expanding in late. A good 
deal of low-level moisture will still be around, so could see a 
continuation of light spotty showers or drizzle. Temperatures Friday 
and Friday night are not expected to budge much, remaining mainly in 
the upper 20s to upper 30s. Temps across the Adirondacks and western 
New England above 1500 feet will likely drop back below freezing at 
night, so could see some lingering icy issues there.
Weak high pressure Saturday may result in skies partially clearing 
and mainly dry conditions. Temps expected to be fairly mild in the 
upper 30s to near 50, or perhaps a bit warmer depending upon the 
amount of sunlight received. Clouds will increase in the afternoon 
ahead of yet another bout of isentropic lift. May even see some 
rain showers breaking out late in the day as the NAM shows. Only 
slight to low chance PoPs over southern zones for now.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The long term period will feature seasonable temperatures with only 
one main threat for wintry mix.
Our period begins Saturday night with a low pressure system from the 
Midwest amplifying as it travels into southern Canada with high 
pressure over eastern Quebec slowly retreating eastward. Upper level 
divergence from a strengthening 300mb jet positioned over the Ohio 
Valley should aid in the low's intensification as the system becomes 
positioned in the jet's right exit region during the second half of 
the weekend. There are still discrepancies among the current 
guidance on how quickly and how strong the low becomes with the GFS 
the most aggressive, showing it cutting off at 500mb with the 
Canadian showing a much weaker wave. The ECMWF was still not 
available for this newest forecast update.
Warm air advection associated with the system should bring 
widespread precipitation into our CWA from southwest to northeast 
Saturday night into Sunday. Given that the antecedent high should be 
positioned well to our north in Quebec leading to east-southeast 
winds over eastern NY/western New England, the air mass ahead of the 
precipitation should be a bit mild with temperatures in the 40s. 
While initial precipitation may be rain in many spots outside of the 
Adirondacks, current guidance suggests cold air damming and 
evaporative cooling transitioning precipitation to wintry mix by 
Sunday morning from north to south. The warm front may be stubborn 
to traverse the area as most guidance shows weak southeast winds 
persisting in the boundary layer until 18z Sunday. Thus, the wintry 
mix may continue thru the first half of Sunday. By 18z Sunday, the 
850mb jet strengths to 40-50kts which may help warm air mix into the 
boundary layer as the warm sector moves closer to our CWA. Thus, 
there is more confidence in the precip type changing to rain after 
18z Sunday but still this is a low confidence forecast as cold air 
is often stubborn to scour out. The GFS and Canadian both show a 
secondary low developing in southern New England Sunday afternoon 
which would keep the warmest air of the warm sector to our south and 
east. Thus, I knocked Sunday's high temperatures a few degrees to 
reflect this thinking. The cold front should finally move through 
Sunday night, ending the precipitation from west to east. 
High pressure noses into the Northeast from the Ohio Valley in the 
wake of this system which would lead to breezy conditions Monday 
with temperatures slightly above normal in the upper 30s to mid 40s. 
A secondary cold front associated with the 500mb trough axis should 
then arrive by 00z Tuesday with colder air in the 20s following for 
Monday night. Despite northwest flow setting up for the mid-week 
period, temperatures remain seasonable with highs in the mid 30s to 
low 40s and overnight lows in the 20s. Ridging also sets in mid-week 
which should keep eastern NY/western New England mainly dry.
&&
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
VFR ceilings and visibilities are expected through tonight 
until around 10Z-15Z when some intermittent mixed precipitation
is expected to begin at all TAF sites. There could be a mix of 
snow, sleet and rain.
After about 15Z, mixed precipitation is expected to become
steadier and ceilings and visibilities will lower to the 
MVFR/IFR levels. KGFL may have VFR bordering on MVFR since much 
of the precipitation could track mainly south of KGFL. By 
this afternoon, precipitation type should be snow at KGFL and 
KALB but may remain a mix at KPSF and KPOU. Precipitation 
should taper off by 00Z/Fri with conditions potentially 
improving towards the end of the TAF period, especially at KALB 
and KGFL.
North winds at less than 10 Kt are expected through the TAF
period.
Outlook...
Wednesday Night: Moderate Operational Impact. Breezy Chance of SHRA...RA...SN.
Thursday: Moderate Operational Impact. Likely RA...SN.
Thursday Night: No Operational Impact. NO SIG WX.
Friday: High Operational Impact. Likely RA...SN...SLEET.
Friday Night: Moderate Operational Impact. Likely RA.
Saturday: Moderate Operational Impact. Chance of RA.
Saturday Night: Moderate Operational Impact. Chance of RA.
Sunday: High Operational Impact. Likely RA.
&&
.HYDROLOGY...
A cold front tracking through the region this afternoon and 
evening will usher in more seasonable temperatures tonight into 
Thursday, with temperatures falling below freezing over the 
Adirondacks tonight and ending the runoff from snowmelt. Will 
maintain Flood Watch over the Adirondacks and western Mohawk 
Valley as the Mohawk at Little Falls has risen a bit lately, but
the overall flood threat in these areas appears to be 
diminishing.
We will also continue to monitor where current ice jams are in 
place for possible movement through tonight. Flooding has occurred 
in areas near the Stockade in Schenectady and Scotia due to water 
backing up near the ice jam on the Mohawk. Parts of this ice jam 
have broken up, but it is unclear whether this will result in 
additional flooding or water levels receding. Water levels will 
continue to be monitored, and additional flood products will be 
issued if necessary.
Snow and wintry mixed precipitation is expected Thursday, with a 
quarter to half inch of QPF expected mainly along and south of I-90. 
More rounds of precipitation are expected Friday into the weekend. 
Current forecasts call for around a quarter to three quarters of an 
inch during this timeframe, highest south of I-90. This may result 
in additional river rises. Temperatures are expected to average 
above normal during this time, but not as warm as we have seen the 
last two days.
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.
&&
.CLIMATE...
High temperature records were broken in many areas on 
Wednesday.
KALB reached 73 degrees at 244 PM EST
KGFL reached 66 degrees at 243 PM EST
KPOU reached 76 degrees at 415 PM EST which broke the all-time
February high temperature.
Wed Feb 21st Previous record highs:
KALB 65F set in 1981
KGFL 65F set in 1981
KPOU 67F set in 1953
All-time February highs:
KALB 74F set Feb. 24, 2017
KGFL 70F set Feb. 25, 2017
KPOU 73F set Feb. 24, 2017
RECORDS FOR KPOU DATE BACK TO 1949... HOWEVER...DATA IS MISSING
FROM JANUARY 1993 - JULY 2000.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Winter Weather Advisory from 4 AM early this morning to 6 PM 
     EST this evening for NYZ047-051-058-063.
MA...None.
VT...None.
&&
$$
SYNOPSIS...11/JPV/JVM
NEAR TERM...BGM/11/NAS
SHORT TERM...Thompson
LONG TERM...Speciale
AVIATION...NAS/JVM
HYDROLOGY...Thompson/JPV/JVM
CLIMATE...