Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 171823

Area Forecast Discussion
National Weather Service Northern Indiana
223 PM EDT Tue Apr 17 2018

Issued at 117 PM EDT Tue Apr 17 2018

A few peaks of sunshine are expected this afternoon as high
pressure approaches from the west. Overnight, look for mostly
clear skies and temperatures in the upper 20s. Warmer on Wednesday
with light rain in the afternoon. This rain can change to snow by
early Thursday morning with little to no snow accumulation. Dry
weather moves in with gradual warming through the end of the week.


.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 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 130 PM EDT Tue Apr 17 2018

Northwest flow off the lake is forecast to continue for the next
several hours at SBN. Thinking of some lake enhancement, I have
opted to allow MVFR ceilings through 23Z...though as I type this I
see a special METAR indicating VFR ceilings have arrived at SBN. I
will continue to monitor such ceilings over the next few hours.

Otherwise, for both TAF sites, expect cloud cover to gradually
decrease and gusty winds from the northwest to relax. As high
pressure scoots through overnight, calm winds will veer and become
east-southeasterly near daybreak.

Lowering ceilings and rain approach at the very end of the TAF


LM...Small Craft Advisory until 5 PM EDT this afternoon for LMZ043-




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