UK AG Weather Center

Winter Precipitation Forecasting Checklist


SNOW DECISION CHECKLIST

These checklists are used to give the weather forecaster a quick and easy way to evaluate liquid vs. solid precipitation. Keep in mind these checklists are not all inclusive, further analysis is required to determine amount and duration of any expected signifigant weather event.

ITEM #1	ITEM #2	ITEM #3	ITEM #4
Surface Temp	Surface Dewpoint	850mb Temp	Freezing Level
<2.2 C (36F)	<3C (37)	< 0C (32F)	< 1200 + or - 300
Yes / No	Yes / No	Yes / No	Yes / No

If ITEM 1 through 4 are No, snow is extremely unlikely. If ITEM 1 through 4 are Yes, continue to the Detailed Snow Checklist

DETAILED SNOW CHECKLIST

PARAMETERS	RAIN	MIXED	SNOW
Surface Temp	> 37F	33F-36F	<33F
Surface Dewpoint	>38F	27F-37F	<27F
850mb Temp	>0C	-2C-0C	<-2C
850mb Dewpoint Dep	****	****	-5C-0C
700mb Temp	-6C	****	<-5C
700mb Dewpoint Dep	****	****	>-11C
500mb Temp N of 40'N	****	****	<-29C
S of 40' N	****	****	<-19C
1000-850mb	>1325m	1300-1325m	<1300m
1000-700mb	>2870	2800-2870m	<2800m
1000-500mb	>5490m	5360-5490m	<5360m
850-700mb	>1555m	1520-1555m	<1520m

FREEZING PRECIPITATION DECISION CKECKLIST

ITEM #1	ITEM #2	ITEM #3	ITEM #4	ITEM #5
Surface Temp	Surface Temp/TD Spread	Surface to <1200m Layer	1200m to >1600m Layer	1200 to <1600m Layer
< 1C	< 8C	>1C	-1C	-1C
Yes / No	Yes / No	Yes / No	Yes / No	Yes / No

If ITEM 1,2,3, and 5 are yes, sleet is likely (note: 1000-500mb thickness should be 5330-5410). If ITEM 1,2,3, and 4 are yes, complete the Detailed list.

DETAILED FREEZING PRECIPITATION CHECKLIST

PARAMETER	IDEAL RANGE	EXTREME RANGE
Surface Temp	0C to -4C	1C to -11C
Surface Dewpoint	0C to -5C	0C to -13C
Surface Temp/TD	< 4C	<8C
850mb Temp/TD	< 2C	< 7C
850mb Temp	+1C to +6C	-8C to +15C
1000-850mb	****	1300 to 1325m
1000-500mb	5330 to 5440m	5320 to 5520m
850-700mb Wind Direction	****	1540 to 1555m

If most parameters are in the ideal range, expect heavier amounts of freezing precipitation. If most parameters are in the extreme range, use the graph to determine the most likely precipitation.