Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
319 PM EDT Wednesday Apr 16 2014

Short term... tonight

The region of snow now extending across portions of Minnesota/northern WI/western
Upper Michigan is associated with a compact middle level wave rotating into
the upper Midwest. The surface low located over the NE/Iowa border will
lift into western Wisconsin by Thursday morning as the middle level wave lifts
up toward western Upper Michigan. The overall trend with this system through
the night will be for gradual weakening as the middle level wave
dampens. Some radar returns within a middle cloud deck have been
advancing across west-cntl lower Michigan this afternoon. A region of weak
ascent along the 285-295k surfaces in advance of the middle level wave
is responsible for these returns. Thus far no precipitation has been
reported over lower Michigan as a departing low level anticyclone is
sustaining a healthy amount of low level dry air. The isentropic
ascent will largely pass north of the Tri Cities this evening. A
broad region of low level warm air advection associated with this
system will overspread Southeast Michigan tonight. Strengthening low level southeast
flow during the night will actually sustain a good degree of dry air
in the low levels which will keep Southeast Michigan precipitation free. Despite the
cool afternoon temperatures and very low surface dewpoints /in the teens
attm/... the increasing gradient overnight /950mb winds forecast to
rise to 35 kts/ will hinder the amount of boundary layer decoupling.
This remains supportive of current forecast min temperatures on the high
side of guidance...mainly in the low 30s.

&&

Long term...Thursday through Wednesday

High pressure will slide off to the east as a weakening low pressure
system tracks across northern Michigan. Precipitation associated
with this low will remain north of the County Warning Area...however expect clouds
to increase over Southeast Michigan especially north of I-69. As a
result of the increased cloud cover through Thursday...have lowered
temperatures a couple degrees /highs expected in the middle to upper 50s/.

A frontal boundary still looks to impact Southeast Michigan on
Thursday night and intensify into Friday as a Theta-E boundary
slides across the region. This front will bring rain showers for
Thursday night and Friday. Current model runs are showing
consistency about the timing of this front and therefore have bumped
probability of precipitation up to likely from Thursday night through Friday. High
temperatures on Friday will be well into the middle 50s however...cold
air filters in behind the frontal passage. 850 mb temperatures show
temperatures dropping temperatures into the 0 c to -4 c resulting in
surface temperatures in the middle to low 30s on Friday night. The
majority of the precipitation is anticipated to move out of the
region by 00z Saturday...but any lingering showers present into
Friday night could be a rain/snow mix as the temperatures drop.

Saturday will bring a rapid increase in 850 mb temperatures from -2 to +6 as
strong warm air advection sets up from return flow. As high pressure departs to the
east...a frontal boundary and elongated low pressure trough will
cross the area on Sunday. The narrow frontal zone and surrounding dry
air will keep showers spotty for the day. Cold air advection will
ensue for next week with mainly dry conditions.

&&

Marine...

High pressure slides east tonight as low pressure enters the western
Great Lakes. Winds are expected to remain below 30 knots tonight and
Thursday as this low builds over the eastern Great Lakes. Lighter
winds will return Thursday night into Friday as a cold front slowly
moves through the area...bringing with it a chance of rain and
possibly some snow showers over Northern Lake Huron. High pressure
returns for Saturday before the next disturbance impacts the
northern Great Lakes on Sunday.

&&

Aviation...issued 103 PM EDT Wednesday Apr 16 2014

//discussion...

Very dry air in the low levels will persist across Southeast Michigan through
Thursday morning. This dry air is associated with surface high pressure
which will track from the eastern Great Lakes this afternoon to northern New
England by Thursday morning. Thus any precipitation and lower cloud cover
associated with the storm system now rotating across the upper
Midwest will remain well northwest of the Southeast Michigan terminals. So the
only aviation weather related item of interest will be a gradual
backing of the S-southeast winds to the east during the course of the
evening.

//Dtw threshold threats...

* none

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.

&&

$$

Short term...SC
long term....rk/mm
marine.......rk
aviation.....SC



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