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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
646 am EDT sun Apr 20 2014



VFR conditions will hold through the taf cycle as deep layer of dry
air in the low levels will keep skies clear below 15kft. Winds will
remain light as they slowly veer from southeasterly to southwesterly
through the period.

//Dtw threshold threats...

* none


Previous discussion...issued 337 am EDT sun Apr 20 2014

Short and tonight

A split flow pattern will keep an active northern stream of the jet
across southern Canada...brushing the northern Great Lakes.
Meanwhile a pair of upper level lows embedded in the southern stream
are lumbering along across the southern Continental U.S. With the western low
forecast to drift north toward Michigan. For today this all leaves light
flow and a surface high sprawling across the eastern Great Lakes and
across the NE Continental U.S.. middle level height will pretty much stay where
they are at as zonal flow is setting up over the region. The high
will steer a surface low up and around it taking it through northern
Ontario today. It will lay out a frontal boundary across northern
Michigan but will not be able to make much progress across the state with
the blocking high in place thus it will end up orientating itself
parallel to the flow /W to east/ keeping it to our north with the
majority of the precipitation. Low level flow will veer to the SW today
allowing warm air advection regime to kick in with mostly clear skies and middle April
sun. With mixing depths approaching 850mb where temperatures are near
10c...most places should make a good run at 70 degrees with western
most counties into the low 70s. The Saginaw Valley will be a close
call as high clouds will be more of a player up there. If clouds can
hold off or stay thin...they too should will make a run at 70. On
the other hand if clouds move in a little faster and thicken up they
will likely be held in the middle 60s. Not a bad Spring day regardless.
Pattern will remain largely unchanged tonight as clouds slowly March
southward. Temperatures should remain elevated in the upper 40s overnight
with continued warm air advection...increasing clouds and increasing ll moisture
with dewpoints holding in the low 40s. May get a few drops of rain
across the Saginaw Valley toward morning but confidence is not
overly high with that so just a slight chance.

Long term...Monday through next Saturday

After slowing further in 12z model suite...low pressure and trailing
cold frontal passage timing remain pretty consistent in the recent 00z suite
as weak low pressure passes over northern lower Michigan late Monday
and the ensuing cold front sags southeast through the DTX County Warning Area Monday
evening into the overnight. Will maintain current configuration of
probability of precipitation and weather as best chance of rain showers still appears to center
in the 02z-08z time window with a small chance of thunderstorms late
in the afternoon/early evening after daytime temperatures climb into
the Lower/Middle 70s and allow for at least marginal instability.

Temperatures will cool notably into the middle of the week as upper
troughing amplifies significantly over the northeast Continental U.S. As this
system phasing into the polar jet stream as it lifts to New England
and southern Quebec. Highs temperatures will fall back into the 50s
to around 60 Tuesday and Lower/Middle 50s Wednesday as high pressure
builds into area behind this exiting storm system...with decent
radiational cooling with this high also leading to widespread 30s
for low temperatures.

Temperatures then moderate into late week as shortwave ridging
translates across the area in advance of the next developing storm
system over the northern plains/upper Midwest. The evolution of this
system to the north/northwest of the area will maintain a mild and
unsettled airmass into Friday as colder air is held at Bay until
next weekend after the system winds down as shifts east through
Ontario/Quebec. While the main forcing from the system over lower
Michigan will occur Thursday night as southern stream shortwave is
drawn northeast around developing upper low...unsettled weather will
persist into the weekend as this upper low is slowly stretched east
to the coastal North Atlantic.


Conditions will remain relatively quiet as high pressure builds off
to the east and a frontal boundary sags south and stalls over the
northern part of Lake Huron tonight after low pressure passes to the
north over southern Canada. The passage of a second low pressure
system by late Monday will allow this frontal boundary to surge
south Monday night into Tuesday as colder air filters southeast
through the Great Lakes. North to northwest flow will increase into
the 20 to 30 knot range over Lake Huron as this colder air builds
south...and while gales are not expected...small craft advisories
may eventually need to be considered in the Tuesday/Tuesday night

High pressure will then bring calming conditions through the middle
of the week before southwest to west winds increase late in the
weekend with the development of the next low pressure over the upper
Midwest and northern Great Lakes.


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



short term...drk
long term....dg

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