Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260803_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 08/03 06Z 0.20 1823  91  99  15 0.00
Mon 08/03 07Z 0.16 1825  95  97  15 0.01
Mon 08/03 08Z 0.18 1826  97  91  16 0.02
Mon 08/03 09Z 0.17 1825  98  86  16 0.12
Mon 08/03 10Z 0.31 1926  98  86  16 0.08
Mon 08/03 11Z 0.42 2026  96  73  16 0.02
Mon 08/03 12Z 0.53 2128  97  75  17 0.01
Mon 08/03 13Z 0.64 2126  99  80  16 0.09
Mon 08/03 14Z 0.66 2224  99  72  16 0.04
Mon 08/03 15Z 0.69 2221  99  65  16 0.03
Mon 08/03 16Z 0.76 2221  98  70  16 0.02
Mon 08/03 17Z 0.83 2121  95  61  16 0.01
Mon 08/03 18Z 1.02 2123  96  77  16 0.05
Mon 08/03 19Z 1.03 2330  90  59  15 0.12
Mon 08/03 20Z 1.49 2429  90  38  14 0.00
Mon 08/03 21Z 1.44 2529  93  51  12 0.00
Mon 08/03 22Z 1.24 2729  97  68  12 0.02
Mon 08/03 23Z 1.19 2830  96  78  10 0.02
Tue 08/04 00Z 0.96 2931  96  75  10 0.02
Tue 08/04 01Z 0.71 3029  97  54  10 0.03
Tue 08/04 02Z 0.49 3129  97  15  10 0.02
Tue 08/04 03Z 0.41 3231  84   3  10 0.00
Tue 08/04 04Z 0.46 3230  75  17  10 0.00
Tue 08/04 05Z 0.63 3026  87  14  10 0.00
Tue 08/04 06Z 0.66 3028  84   2  11 0.00
Tue 08/04 07Z 0.67 3027  80   3  11 0.00
Tue 08/04 08Z 0.69 3026  75   4  11 0.00
Tue 08/04 09Z 0.70 3025  71   3  11 0.00
Tue 08/04 10Z 0.61 3124  67   3  11 0.00
Tue 08/04 11Z 0.50 3022  61   2  12 0.00
Tue 08/04 12Z 0.40 3122  57   2  13 0.00
Tue 08/04 13Z 0.33 3119  55   2  13 0.00
Tue 08/04 14Z 0.31 3117  54   2  13 0.00
Tue 08/04 15Z 0.33 3114  55   2  13 0.00
Tue 08/04 16Z 0.33 3112  55   2  12 0.00
Tue 08/04 17Z 0.37 3009  56   2  13 0.00
Tue 08/04 18Z 0.57 2907  60   2  13 0.00
Tue 08/04 19Z 0.88 2706  64   1  13 0.00
Tue 08/04 20Z 0.58 2506  63   1  14 0.00
Tue 08/04 21Z 0.34 2506  58   1  14 0.00
Tue 08/04 22Z 0.28 2406  56   1  15 0.00
Tue 08/04 23Z 0.25 2407  53   1  15 0.00
Wed 08/05 00Z 0.31 2409  53   2  15 0.00
Wed 08/05 01Z 0.32 2410  56   2  16 0.00
Wed 08/05 02Z 0.36 2411  55   2  16 0.00
Wed 08/05 03Z 0.40 2413  52   2  16 0.00
Wed 08/05 04Z 0.38 2412  51   2  16 0.00
Wed 08/05 05Z 0.36 2512  48   2  16 0.00
Wed 08/05 06Z 0.36 2513  48   2  16 0.00
Wed 08/05 07Z 0.37 2613  52   2  16 0.00
Wed 08/05 08Z 0.35 2612  50   2  15 0.00
Wed 08/05 09Z 0.35 2711  57   3  15 0.00
Wed 08/05 10Z 0.33 2610  63   3  14 0.00
Wed 08/05 11Z 0.28 2609  63   2  14 0.00
Wed 08/05 12Z 0.26 2508  62   1  14 0.00
Wed 08/05 13Z 0.31 2508  68   2  14 0.00
Wed 08/05 14Z 0.32 2408  71   2  13 0.00
Wed 08/05 15Z 0.39 2407  74   2  13 0.00
Wed 08/05 16Z 0.55 2306  71   3  14 0.00
Wed 08/05 17Z 1.05 2207  68   5  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.73 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1