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Area forecast discussion 
National Weather Service northern Indiana
749 PM EDT Monday Apr 27 2015

issued at 740 PM EDT Monday Apr 27 2015

Clearing skies and diminishing winds will set the stage for frost
across much of the region. The greatest risk for frost will likely
be across much of northern Indiana into southwestern lower
Michigan as lows fall into the lower to middle 30s. Temperatures
will rebound on Tuesday with highs reaching into the lower 60s in
most locations. Areas along the Lake Shore will see much cooler


issued at 734 PM EDT Monday Apr 27 2015

Current headlines appear on track for the time being.

Skies were clearing as expected across western areas where the
frost advisory was already in place. Some concerns that sky cover
may clear out more than previously thought in the east which could
increase the threat. Patchy frost should work for the most
part...but some sheltered areas could see larger coverage of frost
by morning.


Short term...(this evening through tuesday)
issued at 350 PM EDT Monday Apr 27 2015

Cloud cover and associated impact on overnight lows/frost
potential are the main concerns for this short term period.
Cool/moist low level cyclonic flow in the wake of robust shortwave
diving through the eastern Great Lakes has led to a fair amount of
stratocu this afternoon. Low level flow does become more
anticyclonic overnight but forecast soundings indicate a decent
subsidence inversion around 850-700mb that will slow the diurnal
dissipation of present cloud cover. Still expect some clearing
overnight...especially in our western counties where clouds are
already scattered...but will take some time in our eastern County Warning Area
based on latest model relative humidity fields. This makes the precise overnight
lows difficult to predict...especially given weak pgf winds of 5
miles per hour or less. Latest consensus guidance is around middle 30s but a
degree or two in either direction will mean the difference between
frost or no frost. Stayed close to prior forecast of upper 30s in
the east and low/middle 30s in the west based on expected cloud
trends. Given light winds...clearing skies...and min temperatures in the
low-middle 30s...feel frost advisory is necessary for at least our
northwest third. Much lower confidence our east/southeast counties will
clear out and see any frost so will hold off on those for now and
just mention patchy frost. Later shifts can make adjustments
based on cloud/temperature trends overnight.

Another dry day on tap for tomorrow as middle/upper level ridging
slides over the Great Lakes. Another round of diurnal cumulus will lead
to just partly sunny skies during the afternoon but 850mb temperatures do
climb a degree or two above zero and this should allow highs to
reach the 60 degree mark.


Long term...(tuesday night through monday)
issued at 350 PM EDT Monday Apr 27 2015

Focus of the long term period is precipitation chances Wednesday night
through Thursday...and a warmer more active pattern next weekend.

Northern stream vorticity/jet maximum will dig southward from eastern
Manitoba/western Ontario Tuesday night through the Great Lakes
Wednesday/Wednesday night. Upper shortwave will deepen and cut off
over the Great Lakes region...which will then dig southeastward
towards the southeast Atlantic coast Thursday night...phasing with shearing
southern stream shortwave. As this low traverses almost directly
over the area...precipitation chances will increase late Wednesday through
Thursday. GFS has been most aggressive/deeper West/ Cutoff low
evolution than other models...however 12z European model (ecmwf)/NAM/Gem starting to
trend toward this more aggressive solution. Therefore increased probability of precipitation
across the eastern half of the forecast area Wednesday night and
Thursday...and introduced slight chance probability of precipitation in the Wednesday period.

After this system moves southeast of the region Thursday
night...ridging will work eastward into the area on Friday...with
dry conditions and a warming trend into the weekend. Backed off with
slight chance probability of precipitation Friday night and Saturday...with an increase in
probability of precipitation into Sunday through sharp moisture increase across
the area and weak disturbances in quasi zonal flow will increase
precipitation chances. However...with weaker overall forcing
signal...will need to continue to watch this period for precipitation


Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 734 PM EDT Monday Apr 27 2015

Diurnal cumulus quickly dissipating...leaving behind little more than
some cirrus. Winds will decouple and become light this evening.
Nam12 cumulus rule shows cumulus field rapidly developing by middle morning
across the area with scattered-broken coverage. Some hints of Lake Shadow
into ksbn my middle to late afternoon which would clear skies out.
Tafs have trended that way...but regardless VFR conditions to


Iwx watches/warnings/advisories...
in...frost advisory from 2 am EDT /1 am CDT/ to 9 am EDT /8 am CDT/
Tuesday for inz003>006-012>016-020-022.

Michigan...frost advisory from 2 am to 9 am EDT Tuesday for miz077>080.

Lm...Small Craft Advisory until 8 PM EDT this evening for lmz043-046.



short term...agd

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