Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 180542

Area Forecast Discussion
National Weather Service Northern Indiana
142 AM EDT Wed Apr 18 2018

Issued at 142 AM EDT Wed Apr 18 2018

Clouds will be on the increase today followed by light rain
overspreading the region later this afternoon. High temperatures
will range from the lower 40s across southern Lower Michigan to
the lower 50s into central Indiana. Colder air will move in as a
frontal system tracks to our south overnight. The rain will change
to snow with an inch or less accumulation over Lower Michigan into
far northern Indiana. Look for an extended dry period Thursday
into early next week with temperatures gradually moderating into
the 60s.


.SHORT TERM...(This Evening through Thursday)
Issued at 217 PM EDT Tue Apr 17 2018

Lake effect snow showers will finally come to an end to begin the
short term period as weak surface ridging builds in from the west
and cyclonic flow from vertically stacked system continues to
lift out to the northeast. Weakening gradient and clearing skies
will lead to shallow surface based inversion and good radiational
cooling tonight as lows drop into the mid 20s over much of the
area...exception being around 30 far SW CWA owing to modest WAA
and increase in clouds late tonight. Focus then shifts to
developing system in the Rockies that will impact our area
Wednesday afternoon/night. Decent mid/upper level speed max
rounding base of upper trof in the four corners will lead to
closed mid level circulation forming as system moves into the
plains tonight. Surface low will track northeast out of the
southern plains into the mid MS valley by Wednesday morning with
models trending to a more southerly track through central Indiana
as upper low opens up and becomes absorbed into the longwave trof
as it moves into the southern great lakes. While return flow
moisture will be lacking as surface ridging extends across the
gulf...more southerly track will place our northern CWA in more
favorable mid level deformation and bring potential for up to a
quarter inch of rain to the northern tier. Forecast soundings
indicating diminishing surface based warm layer Wednesday night
will have rain mixing with and changing over to snow after
midnight. Impressive 150m height falls ahead of upper trof will
place NE CWA in favorable area for a brief period of moderate
snow. Despite calendar...nocturnal timing will have potential for
a quick half to one inch accumulation. Lingering cyclonic flow
Thursday morning will quickly translate E/NE as surface ridging
builds in from the west.


.LONG TERM...(Thursday Night through Tuesday)
Issued at 217 PM EDT Tue Apr 17 2018

Extended period of dry weather along with gradually moderating
temperatures to highlight the long term period. System coming
onshore Wednesday night will dig into southern California and move
into the four corners this weekend as it becomes detached from
the northern stream flow. Meanwhile high pressure builds into the
great lakes region providing fair weather through the weekend and
into the beginning of next week. Little change in airmass on
persistent cool easterly flow will have a slow moderation in
temperatures. Low level thermal trof shifts east as 850mb temps
creep back toward 0C on Friday. Forecast soundings indicate
adiabatic mixing from just below 850mb will yield highs in the
lower 50s. Mid level ridging and height rises expected over the
region by Sunday ahead of northern stream system moving across
Canada which will get highs closer to 60. Continued dry with near
normal temps beginning next week.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
Issued at 138 AM EDT Wed Apr 18 2018

Focus on deterioration of flight conditions across northern
Indiana through the forecast period. Plains mid level circulation
to quickly translate eastward into southern portion of Upper
Great Lakes by end of forecast period. Attendant/resultant
cyclogenesis to southeast of mid level circulation to provide
focus for overspread of light rain late this afternoon, with
passage of triple point well south this evening providing
sufficient column cooling for light snow coincident with IFR
dominant ceilings.





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