Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260402_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 04/02 18Z 0.10 1509  95  70   0 0.00
Thu 04/02 19Z 0.14 1412  94  77   0 0.00
Thu 04/02 20Z 0.15 1414  94  83   0 0.00
Thu 04/02 21Z 0.15 1515  93  86   0 0.00
Thu 04/02 22Z 0.15 1517  94  96   0 0.00
Thu 04/02 23Z 0.15 1520  94  99   1 0.00
Fri 04/03 00Z 0.11 1623  96  98   1 0.02
Fri 04/03 02Z 0.05 1726  96  91   3 0.03
Fri 04/03 03Z 0.03 1728  97  90   3 0.02
Fri 04/03 04Z 0.03 1831  97  90   4 0.02
Fri 04/03 05Z 0.08 1833  97  89   5 0.05
Fri 04/03 06Z 0.12 1933  97  81   7 0.05
Fri 04/03 07Z 0.18 2034  97  72   8 0.04
Fri 04/03 08Z 0.21 2034  96  71   9 0.03
Fri 04/03 09Z 0.24 2036  96  84  10 0.03
Fri 04/03 10Z 0.30 2139  96  87  10 0.03
Fri 04/03 11Z 0.34 2140  95  89  11 0.03
Fri 04/03 12Z 0.40 2241  97  88  11 0.03
Fri 04/03 13Z 0.43 2239  96  91  11 0.05
Fri 04/03 14Z 0.47 2239  98  90  11 0.04
Fri 04/03 15Z 0.54 2339  96  89  11 0.05
Fri 04/03 16Z 0.60 2439  94  75  11 0.03
Fri 04/03 17Z 0.65 2438  95  81  11 0.01
Fri 04/03 18Z 0.71 2438  95  78  11 0.01
Fri 04/03 19Z 0.76 2538  95  78  11 0.01
Fri 04/03 20Z 0.83 2538  95  46  11 0.01
Fri 04/03 21Z 0.95 2538  94  42  10 0.00
Fri 04/03 22Z 1.05 2539  93  47  10 0.00
Fri 04/03 23Z 1.11 2541  94  31  10 0.00
Sat 04/04 00Z 1.21 2541  96  20   9 0.00
Sat 04/04 01Z 1.34 2543  95  13   9 0.01
Sat 04/04 02Z 1.34 2641  92  11   8 0.02
Sat 04/04 03Z 1.31 2640  93  10   7 0.02
Sat 04/04 04Z 1.11 2737  90  12   6 0.02
Sat 04/04 05Z 0.92 2735  87  21   5 0.03
Sat 04/04 06Z 0.74 2833  85  34   4 0.02
Sat 04/04 07Z 0.57 2929  85  26   3 0.01
Sat 04/04 08Z 0.43 3025  87  19   2 0.01
Sat 04/04 09Z 0.31 3122  89  23   2 0.01
Sat 04/04 10Z 0.19 3218  89  21   1 0.01
Sat 04/04 11Z 0.13 3415  89  24   1 0.01
Sat 04/04 12Z 0.10 3512  90  24   1 0.01
Sat 04/04 13Z 0.10 0109  89  28   1 0.00
Sat 04/04 14Z 0.12 0407  88  30   2 0.00
Sat 04/04 15Z 0.14 0806  88  43   2 0.00
Sat 04/04 16Z 0.15 1107  90  38   1 0.00
Sat 04/04 17Z 0.16 1309  89  40   2 0.00
Sat 04/04 18Z 0.17 1412  88  53   2 0.00
Sat 04/04 19Z 0.19 1515  87  49   2 0.00
Sat 04/04 20Z 0.23 1518  86  39   2 0.00
Sat 04/04 21Z 0.22 1520  86  39   3 0.00
Sat 04/04 22Z 0.15 1622  82  78   4 0.00
Sat 04/04 23Z 0.11 1625  80  97   5 0.00
Sun 04/05 00Z 0.08 1727  83  95   6 0.01
Sun 04/05 01Z 0.08 1730  84  94   6 0.01
Sun 04/05 02Z 0.06 1732  87  93   7 0.00
Sun 04/05 03Z 0.06 1734  89  82   8 0.00
Sun 04/05 04Z 0.05 1836  92  86   8 0.00
Sun 04/05 05Z 0.05 1838  94  88   9 0.01

Run total areal avg QPF for the greens is: 0.80 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