NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260721_1200
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)
=== ===== === ==== ==== === === === ====
Tue 07/21 12Z 0.36 2022  71   3  13 0.00
Tue 07/21 13Z 0.34 2023  66   3  13 0.00
Tue 07/21 14Z 0.23 1922  68   4  13 0.00
Tue 07/21 15Z 0.14 1821  74  22  14 0.00
Tue 07/21 16Z 0.12 1825  84  52  13 0.01
Tue 07/21 17Z 0.11 1730  90  70  13 0.05
Tue 07/21 18Z 0.13 1732  90  50  14 0.00
Tue 07/21 19Z 0.06 1733  92  33  14 0.01
Tue 07/21 20Z 0.09 1734  95  36  14 0.02
Tue 07/21 21Z 0.08 1736  96  24  14 0.01
Tue 07/21 22Z 0.09 1734  96  44  15 0.02
Tue 07/21 23Z 0.08 1732  96  45  16 0.02
Wed 07/22 00Z 0.05 1731  95  71  16 0.02
Wed 07/22 01Z 0.08 1830  95  75  16 0.02
Wed 07/22 02Z 0.27 1930  93  83  16 0.07
Wed 07/22 03Z 0.31 2022  90  83  15 0.14
Wed 07/22 04Z 0.24 2021  90  88  15 0.08
Wed 07/22 05Z 0.26 2023  94  87  15 0.04
Wed 07/22 06Z 0.46 2125  98  67  15 0.02
Wed 07/22 07Z 0.51 2124  98  60  15 0.02
Wed 07/22 08Z 0.66 2226  97  66  14 0.02
Wed 07/22 09Z 0.73 2325  98  65  14 0.02
Wed 07/22 10Z 0.76 2423  98  66  13 0.02
Wed 07/22 11Z 0.77 2522  97  66  13 0.02
Wed 07/22 12Z 0.77 2522  96  61  13 0.02
Wed 07/22 13Z 0.79 2621  94  62  13 0.01
Wed 07/22 14Z 0.75 2521  91  62  13 0.01
Wed 07/22 15Z 0.89 2520  93  60  13 0.01
Wed 07/22 16Z 0.93 2420  94  56  13 0.01
Wed 07/22 17Z 1.00 2420  94  41  12 0.02
Wed 07/22 18Z 1.26 2520  94  22  12 0.03
Wed 07/22 19Z 1.43 2421  89   8  11 0.01
Wed 07/22 20Z 1.25 2521  88  25  11 0.01
Wed 07/22 21Z 1.38 2623  91  25   9 0.01
Wed 07/22 22Z 1.20 2622  89  22   9 0.00
Wed 07/22 23Z 1.15 2723  91  22   8 0.00
Thu 07/23 00Z 1.13 2723  92  23   7 0.00
Thu 07/23 01Z 1.04 2824  92  23   7 0.01
Thu 07/23 02Z 1.01 2825  93  25   6 0.00
Thu 07/23 03Z 0.94 2924  95  25   6 0.01
Thu 07/23 04Z 0.77 3023  92  24   5 0.01
Thu 07/23 05Z 0.64 3023  89  19   5 0.00
Thu 07/23 06Z 0.55 3123  87  19   6 0.00
Thu 07/23 07Z 0.49 3122  84  17   5 0.00
Thu 07/23 08Z 0.43 3221  78  18   5 0.00
Thu 07/23 09Z 0.36 3217  73  24   6 0.00
Thu 07/23 10Z 0.38 3113  71  35   6 0.00
Thu 07/23 11Z 0.41 2911  72  43   6 0.00
Thu 07/23 12Z 0.45 2712  74  42   6 0.00
Thu 07/23 13Z 0.50 2713  75  39   6 0.00
Thu 07/23 14Z 0.58 2714  74  34   6 0.00
Thu 07/23 15Z 0.71 2713  69  30   7 0.00
Thu 07/23 16Z 1.03 2712  64  30   7 0.00
Thu 07/23 17Z 3.09 2711  67  29   8 0.00
Thu 07/23 18Z 3.77 2709  72  25   8 0.00
Thu 07/23 19Z 4.56 2609  75  21   8 0.00
Thu 07/23 20Z 5.01 2709  77  20   9 0.00
Thu 07/23 21Z 4.01 2708  77  21   9 0.00
Thu 07/23 22Z 2.65 2708  78  21   9 0.00
Thu 07/23 23Z 1.37 2707  78  22   9 0.00

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