FORECASTING SNOW

SNOW VERUS RAIN
1. Synoptic indications: Rain _______ Freezing Rain _______ Snow _______ Mixed _______

2. Freezing Level: 1200 feet or higher = Rain _______ 1200 feet or lower = Snow _______

3. Thickness values:

A. 1000-850MB Low south of Japan Leeside trough

_______ Rain 1308 meters of more 1303 meters or more
_______ Mixed 1307-1290 meters 1303-1295 meters
_______ Snow 1289 meters or less 1294 meters or less


B. 1000-700MB

_______ Rain 2829 meters or more 2798 meters or more
_______ Mixed 2828-2795 meters 2797-2785 meters
_______ Snow 2796 meters or less 2784 meters or less


C. 1000-500MB

_______ Rain 5381 meters or more 5287 meters or more
_______ Mixed 5380-5326 meters 5286-5261 meters
_______ Snow 5325 meters or less 5260 meters or less


D. 850-700MB

_______ Rain 1522 meters or more 1500 meters or more
_______ Mixed 1521-1500 meters 1499-1490 meters
_______ Snow 1499 meters or less 1489 meters or less

4. Temperature

Snow= less than 33.7 degrees F.
Mixed= 33.8-38.5 degrees F. (See Note 2)
Rain= 37.8 degrees F. or greater (See Note 3)

5. 850MB temperature/dewpoint/wetbulb

A. Temperature Current _____C Forecasted _____C

-03 degrees C or warmer=Rain _____C
-07 degrees C or colder= Snow _____C


B. Dewpoint: Current _____C Forecasted ______C(Note 5)

C. Wetbulb: Current _____C Forecasted ______C

6. 700MB Temperature

-11 degrees C or lower =snow
-10 degrees C or warmer =rain


(Use top of MT. Fuji as basis for hourly 700MB Temperature check)

8. Boundary layer winds

1000 ft _____ 2000 ft _____ 3000 ft _____
Northwest through east-northeast = Favorable for snow; Use PPBB upper air reports.


Step 1. --- Determine the 1000-500MB thickness in meters from the latest upper air sounding. The
station selected will depend upon the advection pattern, but the use of Hamamutsu (47681) to
Tateno (47646) should provide the best results.

Step 2. --- Enter column Hs of table AI (precipitable water (w) and corresponding thickness (Hs)
with the computed 1000-500MB thickness in meters. Determine the amount of precipitable water in
from column W.

Step 3. ---Multiply this figure (W in inches) by 10 to arrive at the accumulation of snow which should
be forecast. (Assume a snow to rain ratio of 10:1)