3:00 pm update: new forecast thoughts

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 First let’s set-up the isentropic part of the forecast, the principle is regions of higher pressure and moisture advections see the best lift thus more precipitation.

midnight tonight 291 K pressure level and mixing ratio map

notice the buldge of the moist and pressure values into western and central Kentucky where colder air is present thus lift is occurring art this time which develops precipitation.

Thursday rush-hour. Notice the higher pressure and mosiutre advections are now over the bluegrass. Also the garcia method applies to the mixing ratios in regions that see all snow of around 4 g/kg this would equate to 8 inches of snow.  the GFS isentropic set-up is about the same.

now on to temeprature profiles.  We’re already at 32 in Bowling Green and in the 20’s across the rest of the region. BWG should fall into the upper 20’s later tonight then rise to 32 around  midnight.

Here is my forecast for furthest north point of 32 line

precipitation type timeline

midnight

6 am

– overall I still think the Isentropic set-up favors the same regions from e-town to 1-64 to Jackson along the mtn pkwy for the best lift. with the 12z ECMWF looking more like the NAM trended the forecast in that direction. Model max qpf is .5-.75 and the garcia method yields about 8 inches of max snowfall.  around .5-.75 liquid should fall in the best lift zone with .25-.5 outside of this zone.

FINAL FORECAST

Zone A: up to 1/10th ice quick change to rain

Zone B: some snow and sleet under an inch .1-.6 of ice before a change to rain between midnight and 6 am. more northeast part of zone and less southwest part of zone

Zone C: 2-6 of snow and sleet and .25- .5 ice. ( you will only see the top end of either ice or snow)

Zone D:  4-8 of snow and sleet with some mixing with ice on occasion. The 8’s should be on the southern edge of the D zone.

– within 40 miles you may go from 8 inches of snow just north of  Frankfort to 5 inches of snow and sleet with .25 ice in Lex to .6 ice just southwest of Richmond.  

Saturday still is a miss, I’m a snow fan as well but a break is needed

– getting the sense monday we may need to break out the isentropic maps again for a smaller event.

– both the 12z gfs and ecmwf have another snow system just before christmas.

white-o-meter: 7/10

By the way MJ was right about the STN WRF accuracy, this model was way to cold today and should not be used for this event. A further investigation of wintertime parameters will be needed for this WRF model at a later date. The model was not supersaturated though. Also make sure to read his NWS discussion today the last of several very good discussions from the NWS in recent days.

4:30 pm update

– moving jefferson, shelby and oldham counties to zone C

– 18z models and RUC showing more icing for BWG.

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4 Responses to “3:00 pm update: new forecast thoughts”

  1. mitchg Says:

    only mixing ratios showing on the map.

  2. tornadolarkin Says:

    Do you think dewpoints will be an issue?

  3. mitchg Says:

    not really saturation should be quick RH is already @ 60%.

  4. rolo Says:

    exxcellent mitch, I dont think ice going be a majior problem and so glad my area in CLAY COUNTY will turn to rain quick. tx man.

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