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Area Forecast Discussion (AFD)

Issued by Albany, NY (ALY)

                            
882 
FXUS61 KALY 192320
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
620 PM EST Mon Feb 19 2018

.SYNOPSIS...
Unseasonably to possibly record warm weather will be around
Tuesday and Wednesday in the wake of a warm frontal passage.
After some showers this evening into tonight, little to no
precipitation is expected for much of the area into midweek
except for over the southern Adirondacks. The combination of
snowmelt and rainfall may lead to some minor flooding over the
higher terrain north and west of Albany. A cold front will cool
temperatures down by Thursday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Flood Watch in effect tonight through Thursday morning for
northern Herkimer, Hamilton, and northern Warren Counties...

Radar showing rain building east but the northern edge has not
reached the southern Adirondacks yet. Trends show the rain
expanding north with a couple of sub mesoscale low level
vortices embedded on the northern edge seen in radar imagery as
well, headed for the southern Adirondacks. So, just some minor 
adjustments to the timing of the expansion of the area of 
rain through tonight. Some minor adjustments to temperatures 
based on current data and trends as well. Previous AFD has a few
more details and is below...

A very amplified flow is over the CONUS with a strong 
anticyclone in place over the southwest Atlantic, and a full- 
latitude trough pushing into the Intermountain West. A 
strengthening low level jet is resulting in isentropic lift 
which is gradually saturating the dry column noted on the 12Z 
KALY sounding. Will continue with categorical PoPs nearly area- 
wide through 00Z. The moisture plume is impressive with PWATs 
around 1 inch over the majority of the forecast area by 00Z. 
Have increased QPF a bit over the favored southwesterly flow 
higher terrain of the western Mohawk Valley/southern 
Adirondacks/southern Vermont (see hydro section below). 
Temperatures aloft above freezing support rain as the dominant 
P-type. Some wet bulbing has cooled temps a bit with the onset 
of the precipitation, but it appears that surface wetbulb temps 
above freezing will greatly limit any icing threat, and the 
current forecast has no mention of ice.

Tonight, chances of rain will diminish south to north, becoming
confined to areas mainly north of the Mohawk Valley after 06Z.
This will occur as low to mid-level winds veer, minimizing
isentropic lift, and with some drier midlevel air arriving. Some
areas of fog or light showers/drizzle cannot be ruled out with
southerly flow allowing for low-level moisture advection to
continue. Temperatures should stay steady or rise somewhat
overnight, solidly in the 40s in most areas by daybreak Tuesday.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Tuesday into Wednesday, the massive upper ridge centered off the
southeast US coast will expand into the Northeast, with a large
area of +2 to +3 SD H500 heights over much of the eastern CONUS.
At lower levels, the warm front and attendant isentropic lift
will continue to push mainly north of the forecast area, mainly
confining rainfall to portions of the southern Adirondacks. With
the influx of low-level moisture, we could see areas of fog or
perhaps drizzle early in the day outside of the area of steadier
rainfall in the Adirondacks. Temperatures are a tricky call. 
The potential for unseasonable warmth is there with H925 temps 
of 10-12C (also +2 to +3 SD), but it will be heavily dependent 
on whether any low clouds can scour out. The NAM keeps these low
clouds around along with an easterly wind component up the 
Hudson Valley, and is nearly 10F cooler than the GFS which mixes
deeper with a southwesterly flow. Sided a bit more toward the 
warmer side for favored downslope areas with a fairly strong SW 
flow at 925 mb, but would not be surprised to see large spatial 
variation in temperatures. 

Very mild Tuesday night as the forecast area remains solidly in
the warm sector with an elongated area of low pressure along the
approaching baroclinic zone well off to our west. Patchy fog is
possible, especially across areas with snowpack as dewpoints
approach 50F. 

On Wednesday, the upper trough deamplifies as it pushes east,
resulting in gradual height falls locally. This will push a cold
front through the forecast area during the evening hours, but
with little upper support, expect nothing more than a broken
band of showers. Have better confidence in widespread very warm
to possibly record high temperatures with the warm air in place
and winds in the low levels veering southwesterly. Feel that
mixing potential is better Wednesday compared with Tuesday, and
sided more toward the warmer MAV MOS rather than the overly cool
MET MOS. This has the potential to put us not only in record
high territory, but possibly near all-time February record highs
(which were set just last year at Albany, Glens Falls, and
Poughkeepsie). One factor that could short-circuit the record 
warmth is if the front and associated cloud cover end up being a
bit quicker than currently anticipated.

A quick drop in temperatures is expected behind the front
Wednesday night. The degree of cooling is still uncertain, with
some guidance suggesting the northern half of the forecast area
falling below freezing by sunrise Thursday. Current forecast
calls for lows in the mid-20s to upper 30s. Mainly rain is
expected with the weakening band of showers, although some snow
could mix in across the higher terrain.

See our Hydro and Climate sections with more details...

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Unsettled pattern setting up Thursday through Monday.  Pieces of 
upper energy track quickly within west southwest upper flow.  There 
are timing differences in sources of guidance and ensembles as the 
boundary layer baroclinic zone oscillates north and south in 
response to the advance and exit of each upper impulse and zone of 
enhanced moisture and forcing.  

First, on Thursday, as a cold front settles south of our region, 
there are hints of one last piece of upper energy that tracks 
through our region, which could support a brief period of snow and 
rain to our area, primarily from the Mohawk River Valley, Capital 
District and southern Vermont and points south.  Just including 
chances since there is not a good consensus and we will know more as 
we get closer. Highs Thursday in the 30s to lower 40s but cooler if 
there is more organized precipitation.

Thursday night should be dry but the next system will approach and 
begin to affect our region Friday, likely impacting our region 
Friday and Friday night. Depending on where the baroclinic zone and 
freezing line sets up, there should be a zone of mixed precipitation 
over our region with rain to the south, snow to the north and the 
mix in a broad zone in between.  There are hints of possible sleet 
and freezing rain but because of the high degree of uncertainty in 
coverage of precipitation and thermal profile of the atmosphere in 
various regions just including rain or snow. Highs Friday in the 30s 
to lower 40s but potentially cooling to around freezing in many 
areas Friday night.

Another period of reduced coverage of clouds and precipitation and 
potential dry weather is possible Saturday and Saturday night but 
keeping small chances with the uncertainties in timing of systems in 
the quick west southwest upper flow. Ensemble probabilities also 
support keeping at least chances for precipitation Saturday and 
Saturday night. Highs Saturday in the 40s but some upper 30s 
northern areas.

Increased coverage of precipitation with another piece of upper 
energy Sunday into Monday but again, precipitation types will be 
determined on where the baroclinic zone sets up and where the 
boundary layer freezing line sets up.  Indicating mostly rain 
chances in the day and mixed rain and snow at night.  There are 
still some hints at some potential sleet or freezing rain but again 
there is a very high degree of uncertainty. Highs Sunday in the 40s 
with around 40 north and mid 40s south.  Highs Monday in the 40s but 
some upper 30s north and possible near 50 south.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
A warm front will approach eastern NY and western New England from 
the Ohio Valley and the Mid Atlantic Region tonight.  This boundary 
will slowly lift north and east of the region tomorrow with periods 
of rain and showers ending.

Ceilings have trended MVFR at KPSF, KPOU and KGFL and will lower
to MVFR at KALB this evening. Rain continues to expand through
the area and as the air at the surface saturates through
tonight, ceilings are likely to lower to IFR as will
visibilities lower intermittently to IFR with steadier rain and
areas of fog.

Conditions will likely improve to MVFR/VFR between 12Z-16Z
Tuesday as rain ends with lingering MVFR/IFR conditions 
persisting the longest at KPSF. Visibilities should remain VFR
through Tuesday afternoon but ceilings may vary between MVFR and
VFR as the warm front will be slow to lift north, keeping 
clouds in the region.

LLWS was included at all the TAF sites overnight with the 2000
Ft AGL winds increasing to 35-45 kt, and the surface winds 
decreasing to 10 kt or less. The LLWS begins at 00Z at KPOU, 
and KPSF, and 04Z-05Z at KGFL and KALB. The LLWS will diminish 
towards daybreak.

The winds will be southerly at 5-12 Kt this evening but some 
gusts near 20 Kt possible at KALB. The winds will lighten to 
less than 10 Kt overnight, and then increase from the south to 
southwest at 7-12 kts late Tuesday morning continuing in the
afternoon.

Outlook...

Tuesday Night: No Operational Impact. NO SIG WX.
Wednesday: Moderate Operational Impact. Breezy Chance of RA.
Wednesday Night: Moderate Operational Impact. Chance of RA.
Thursday: Low Operational Impact. Slight Chance of RA...SN.
Thursday Night: No Operational Impact. NO SIG WX.
Friday: Moderate Operational Impact. Chance of RA...SN.
Friday Night: Moderate Operational Impact. Chance of RA...SN.
Saturday: Moderate Operational Impact. Chance of RA.

&&

.HYDROLOGY...
Temperatures will be well above normal to possibly near record
high levels through Wednesday, not falling below freezing until
Wednesday night at the earliest. Periods of rainfall will affect
the entire forecast area through early tonight before becoming
mainly confined to the southern Adirondacks through Wednesday. A
cold front may bring additional light precipitation Wednesday
evening.

The combination of QPF of 0.50 to 1.50 inches across the
southern Adirondacks, along with 1 to 3 inches of runoff from
snowmelt, will lead to flooding concerns through Thursday
morning. Latest forecasts have rivers rising in the upper
Hudson and western Mohawk basins including the Sacandaga and
Schroon Rivers. The Sacandaga at Hope is forecast to reach 
minor flood stage by Wednesday evening. A Flood Watch is in 
effect for portions of the southern Adirondacks to address flood
potential. There is potential for renewed flooding near the ice
jam on the upper Hudson River near Thurman.

A Flood Watch was not extended into the Schenectady area at this
time due to the light rainfall forecast, potential for a 
gradual melt of the ice with the mild temperatures, and recent
reduction in ice thickness. However, the Mohawk River is likely
to rise from an influx of water from upstream rainfall and 
snowmelt, so additional flooding concerns cannot be ruled out in
the vicinity of the ice jam along the Mohawk. If confidence in
flooding increases, a Flood Watch may be necessary.

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...
Record Warmth is possible TUE into WED.

Feb 20th 
The record highs:
KALB 66F set in 1930 
KGFL 58F set in 1981
KPOU 63F set in 2016

Feb 21st
The 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...Flood Watch from 1 AM EST Tuesday through Thursday morning for 
     NYZ032-033-042.
MA...None.
VT...None.

&&

$$
SYNOPSIS...Thompson
NEAR TERM...NAS/Thompson
SHORT TERM...Thompson
LONG TERM...NAS
AVIATION...NAS
HYDROLOGY...Thompson
CLIMATE...