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Area forecast discussion 
National Weather Service Wilmington Ohio
403 PM EDT Sat Apr 18 2015

high pressure over the area today will begin to pull east and
washout as an upper level low over The Rockies moves east. A warm
front will then lift across the region Sunday afternoon followed
by a cold front Monday evening.


Near term /until 6 am Sunday morning/...
a broad area of high pressure currently located over Ohio has
already started to weaken and washout as a cold front near the
Michigan/ Ohio state line sags south. This front is expected to
stall north of the area Sunday morning as the upper level shortwave in
association with the front quickly pulls east. Also... an area of low
pressure that is clearly seen on infrared and visible satellite this
afternoon will begin to finally get dislodged and push east. A
potent shortwave will slowly start to nudge the low towards the
east Sunday morning. As this happens clouds will start to quickly
thicken tonight into Sunday morning. This will cause lows to be
around 5 degrees warmer Sunday morning than this morning.


Short term /6 am Sunday morning through Tuesday/...
the chance of rain Sunday will begin to quickly increase as waves
of positive vorticity advection move from the Gulf Coast up and around the base of the
upper level low towards Ohio. High res models are showing a broad
precipitation shield ahead of the warm sector arriving into Cincinnati
around 8 am and then expanding to Columbus around 2 PM. Precipitable waters on
the both the GFS and NAM are forecasted to reach 1.65" by Sunday
around noon (nearing 99th percentile for this time of year). Cape
values Sunday will be very low but 0 - 3 km srh values on both the
GFS and NAM soundings are very impressive. Srh values are in the
400 to 600 m2 /s2 range Sunday afternoon as a surface low
approaches from the southwest. As of now expecting precipitation shield
to be mostly warm air advection driven initially with storms not being able to
fully utilize such high low level srh values.

A warm front will then move through the area Sunday afternoon
which will allow for a brief break in the precipitation before the
remnants of the upper level low shear out and move over the area
late Sunday/ early Monday. Sunday afternoon and Monday afternoon a
few thunderstorms will also be possible as cape values come up a
bit. The initial shortwave that dislodged the low over The
Rockies will begin to occlude and push a cold front through the
area Monday evening. The GFS and NAM are in pretty good agreement
with the timing of the front for Monday evening while the Euro
pushes the front through slightly quicker. Given the occlusion
process of the low ongoing at the time have leaned towards the
slower frontal passage. Rain chances will then lessen Tuesday as
drier air moves in from the west.

It will also be breezy the next couple of days as 850 mb winds
are forecasted to be consistently around 40 kts. This will be
thanks to an elevated pressure gradient though the short term.


Long term /Tuesday night through Saturday/...
good agreement between models continuing to exhibit an upper low
over southern Ontario dominating the early/middle extended period
keeping unseasonably cool temperatures and considerable clouds in
especially the northern forecast area. The best chance for showers for
the entire forecast area will come when the surface high in the southeast
United States moves offshore and allows for an elongated cold front
to slowly pass through the area on Wednesday and linger just south of the
forecast area Wednesday night. The upper low finally begins to push east enough
to lose its influence on forecast area by Friday night into Saturday.
Some model differences this far out in the forecast in that the
European model (ecmwf) is more amplified with a southern stream shortwave...bringing
it into the Tennessee and lower Ohio valleys...whereas the GFS keeps it
further south over the Gulf Coast states while continuing to amplify
the departing upper low. Have compromised with chance of precipitation in
especially the southern third of forecast area.


Aviation /19z Saturday through Thursday/...
conditions will remain VFR through the early part of the forecast
as high pressure departs to the east. Clouds will thicken and
winds will increase ahead of low pressure. Showers are expected to
move in from the southwest Sunday morning. Conditions may
deteriorate to MVFR by Sunday afternoon as the boundary layer
becomes saturated under prevailing rain showers. Expect winds
gusting over 20 knots from the east southeast on Sunday. Thunderstorms
may affect cvg later Sunday afternoon when instability is forecast
to increase.

Outlook...MVFR/IFR ceilings and visibilities are possible Monday...with
a chance of thunderstorms.


Iln watches/warnings/advisories...


near term...Haines
short term...Haines
long term...jdr

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