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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
323 am EDT Friday Apr 18 2014

Short term... today and tonight

A weak low pressure system that tracked through northern Michigan Thursday
is forcing a weak cold front through Southeast Michigan at press time. Looking
aloft...heights are lowering as a middle level trough works eastward
with a lobe of vorticity pivoting through lower Michigan. The trough is
fracturing in the sense that an upper low that has been clinging to
the base of the trough finally cuts off over the deep south. A
shortwave seen on water vapor over the plains is shearing apart as
it lifts over the area leading to a midlevel cloud field. Models
continue to advertise an uptick in frontogenesis right over Southeast Michigan
this morning from about 09-12z as the 500mb height fall maximum
flares up over the area inducing the jet to strengthen with the
right entrance region also over the area. So model wise the upper
levels look favorable for some precipitation this morning with some aide in
the low level fgen. A big downfall to the system will be with
moisture. The DTX 00z sounding shows only a half inch of precipitable water in the
column with a deep layer of dry air up to about 9kft. Models are
right on track with this and do up the precipitable waters to around .7 during the
frontal passage. Upstream observation are good for showing the very scattered nature
of the precipitation thus far with a few observation showing light rain or drizzle
with ceilings lowering from 10kft to around 6500ft with the precipitation. The
struggles with dry bl air should continue and have been thus far as
radar returns have been showing up for hours with nothing to show
for it. But as mentioned...the models show the strongest forcing
developing right over head as the upper level players come together
so will continue a band of chance pop working through the area
during the morning hours. Quantitative precipitation forecast will remain low due to the lack of
moisture present to work with.

The rest of the day will show an improving trend as ridging will
quickly fill in behind the front. The longwave pattern is low
amplitude leading to only a small drop off in temperatures behind
the front. The surface high will pass to the north so we should keep a
semblance of easterly flow as winds relax overnight. Skies will
also be clearing which will favor some radiative cooling processes.
Dewpoints will only fall into the upper 20s to low 30s which will
cap off the temperature drop overnight.

&&

Long term...Saturday through next Thursday

Quiet weather is expected over the weekend as high pressure builds
southeast across the area. Temperatures will be cool Saturday under
the influence of this high...but moderate within return southwest
flow on the backside of this system on Sunday...pushing 70f in some
instances.

Mild weather will persist into Monday night/early Tuesday as low
pressure approaches from the Central Plains. This low will develop
as the lead impulse in a string of northern Pacific shortwaves
phases with southern stream shortwave now meandering east towards
Baja California California. As this system encroaches...rain showers will
become more prevalent from Sunday night into Monday and peak in
coverage/intensity Monday night with the passage of the system.

While some colder polar air is pulled south into the area behind
this system...the upper level flow remains zonal...so significant
cooling will be held at Bay with temperatures returning to the 60s
by late week.

After another period of relatively quiet weather during the middle
of the week...the chance of rain showers increases again late in the
forecast period as the next significant surge of Pacific shortwave
energy arrives in the vicinity. This system appears to have a better
chance at phasing with the polar jet stream over southern Canada and
will most likely be a stronger system than the initial low earlier
in the week. While precipitation will remain rain...notably colder
air will filter back into the area just beyond this forecast period.

&&

Marine...

A cold front will filter southeast through the area early today as
weak low pressure tracks into Quebec. Expect scattered showers as
the front crosses the area...but dry weather thereafter as strong
high pressure builds over the central Great Lakes from tonight into
Saturday. Northerly flow in advance of this high will bring a slight
increase in waves tonight into early Saturday...but calmer
conditions will return as the high crosses over the central Great
Lakes early this weekend. However...southerly winds will pick up for
the second half of the weekend...but remain generally under 20 knots
for most areas...as another low pressure system approaches from the
Central Plains.

&&

Aviation...issued 1153 PM EDT Thursday Apr 17 2014

//discussion...

Cold frontal boundary will ease across Southeast Michigan this
morning. Some increase in middle level moisture along the boundary
will bring a chance of showers through middle morning. However the
maintenance of a dry low level environment will ensure conditions
remain in VFR through this time. A modest pre-frontal southerly
wind will shift to northwest with the frontal passage. Clearing
skies Friday afternoon as the boundary exits to the southeast.

//Dtw threshold threats...

* low confidence in a period of ceilings below 5000 feet this morning.

&&

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

&&

$$

Short term...drk
long term....dg
marine.......dg
aviation.....Mr



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