Area Forecast Discussion
Issued by NWS Cleveland, OH

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000
FXUS61 KCLE 220005
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
705 PM EST Wed Feb 21 2018

.SYNOPSIS...
Low pressure will track northeast across the Ohio valley late
tonight and move toward the mid Atlantic coast on Thursday.
Another low pressure system will track northeast into the Great
Lakes region on Friday, lifting a warm front north into the
area. The front will linger across the region through the
weekend until another low pressure system moves into the Great
Lakes on Sunday.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
Rain shield extends over the SERN third of the forecast area, so
bumped up pops to likely. Temps running a little warmer than
forecast so removed all mention of freezing rain before
midnight.

original discussion...
Complex, high uncertainty forecast in the works for tonight as a
wave of low pressure moves northeast along a frontal boundary
situated southeast of the forecast area. Precip will overspread the
region from southwest to northeast late this evening through
tonight. Models have been trending northward with the 12Z runs and
latest hi-res runs, so have expanded cat pops northward for much of
the forecast area tonight.

P-type issues will be a challenge for the late tonight into Thursday
morning period, as surface temperatures along and north of the US-30
corridor are expected to drop just below freezing, with temperatures
near freezing along the US-30 corridor and temperatures just above
freezing south. There will be some warm air overrunning with this
system, and nailing down the transition line will be a challenge.
Guidance shows a wide range of p-type probabilities for most of the
area, so have went with a conservative approach to p-types and
subsequent precip amounts. Persistent northeast low level flow will
help usher in drier air in the lowest 5kft, which will likely lead
to some evaporative cooling effects with the onset of the precip.
Expecting a fairly sharp gradient from frozen precip across the
north to melted/liquid precip south, but given the uncertainty with
where exactly this will set up, went more broadbrushed with p-type
amounts.

As far as impacts go, pavement temperatures are fairly warm across
the area from the recent warmth, so there is a bit of uncertainty
with how quickly, if at all, pavement temps get to freezing where
frozen/freezing precip will be impactful. Playing it fairly safe
with the winter weather advisory, given the uncertainty with p-type,
any snowfall/sleet accums on the northern end, surface air
temperatures and pavement temperatures. For the counties along the
US-30 corridor, expecting the main impacts to be from sleet and
freezing rain, primarily on elevated road surfaces such as bridges
and overpasses. The northern tier of counties in the advisory,
expecting impacts from mainly snow/sleet accumulation of primarily 1
to 2 inches, plus possible trace amounts of ice. This is a fairly
complicated scenario, with some models indicating much heavier
snowfall amounts on the cool side, and some bringing the warm air
aloft further north into the northern part of the forecast area and
keeping freezing rain the primary issue. This will need to be
monitored closely through the evening and overnight with the
progression of surface temperatures, precip onset and p-type. All in
all, thinking the primary impact will be along and north of the US-
30 corridor, with lesser confidence in impacts south of US-30.
Confidence is specific p-type amounts at any given point is fairly
low as well, with current forecast amounts fairly conservative.

Surface temperatures will rise above freezing across most of the
area by midday Thursday, sooner across the southeast part of the
forecast area. Precip is expected to move out of the area fairly
quickly early Thursday afternoon as high pressure builds into the
area. Highs on Thursday will range from the low 40s east to the mid
30s west. The brief dry period Thursday afternoon and evening will
come to an end late in the overnight into Friday morning as another
wave of low pressure track northeast into the area. Precip will
overspread the region from southwest to northeast after 06Z. Surface
temperatures will be near or just below freezing across far
northwest Ohio, so the precip may briefly start out as freezing
rain, however rain is expected elsewhere. Lows Thursday night will
be in the low to mid 30s.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
The short term begins Friday morning with models showing a wave of
low pressure moving northeast out of Indiana to western NY by 18z.
Temperatures will be warming aloft through the night Thursday night
ahead of the low and by 12Z Friday surface temps should be above
freezing so will have precip as all rain. Best chance for precip
should be the first half of the day with models showing drying from
the northwest through the afternoon. Friday night high pressure will
build into the area from the north as the high drifts east across
the Great Lakes. Moisture appears to get pushed south enough to
remove pops from the forecast through the night. We could have light
rain approach from the southwest towards morning but with the parent
low still far west in Kansas am thinking most of the associated
precip would be west of the area through 12z.  For Saturday the low
moves to MO/IA forcing a warm front and associated rain, north into
the area. Best chances south but will have likely pops north and
categorical pops south. Saturday night the associated cold front
moves through so will have categorical pops area wide. Sunday will
be a day of transition with high pressure and cooler drier air
moving in from the west. Will need to begin with pops mainly east
but through the afternoon will dry out the west and drop pops into
the chance category east.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Quiet weather is expected during the period as high pressure builds
over the region for the first part of the workweek.  The precip from
the weekend storm should about be gone by 00z Monday so will start
the forecast out dry.  By late Tuesday the surface ridge will be
east of the area.  Will start to see a gradual increase in clouds by
the end of the period but will maintain dry weather through 00Z
Thursday.  Temperatures will continue to average above normal during
the period with highs mainly in the mid to upper 40s.

&&

.AVIATION /00Z Thursday THROUGH Monday/...
Front near the Ohio River will lift north overnight. rain across
the SERN portion of the area will continue this evening. Precip
will gradually transition to snow overnight. Snow will mix with
or change to wintry mix of freezing rain and or sleet late
tonight. Precip should end or transition to rain by late
morning.

OUTLOOK...Non-VFR likely to dominate most of the time thru Sunday.

&&

.MARINE...
No gales expected through Monday.  Look for north flow turning
northeast overnight at 5 to 15 knots as high pressure builds across
the Great Lakes. Flow will increase to 15 to 20 knots from the
northeast Thursday and Thursday night as the gradient tightens.
friday the high moves east of the lakes turning flow southeast
around 10 knots as the gradient relaxes. Look for light and variable
flow until winds turn easterly Saturday afternoon at 10 to 15 knots.
Saturday night and Sunday deep low pressure will move northeast
across the western lakes forcing a cold front across Lake Erie. Look
for southeast flow to turn southwest and increase to around 20 to 25
knots. Sunday night into Monday the low pulls northeast into Quebec
as high pressure builds into the low Ohio Valley.  Southwest flow
will continue but diminish to around 10 knots.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...Winter Weather Advisory from 1 AM to 1 PM EST Thursday for
     OHZ010-011-013-014-017>023-027>033-036-037.
PA...Winter Weather Advisory from 1 AM to 1 PM EST Thursday for
     PAZ003.
MARINE...None.

&&

$$
SYNOPSIS...Greenawalt
NEAR TERM...DJB/Greenawalt
SHORT TERM...TK
LONG TERM...Kubina
AVIATION...Riley
MARINE...TK



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