NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260323_0600
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)
=== ===== === ==== ==== === === === ====
Mon 03/23 06Z 0.07 0206  93  15  -5 0.00
Mon 03/23 07Z 0.12 0308  92  15  -5 0.00
Mon 03/23 08Z 0.14 0408  93  16  -5 0.00
Mon 03/23 09Z 0.14 0408  94  19  -6 0.00
Mon 03/23 10Z 0.18 0409  95  18  -6 0.00
Mon 03/23 11Z 0.25 0511  96  18  -7 0.00
Mon 03/23 12Z 0.34 0612  97  19  -8 0.01
Mon 03/23 13Z 0.43 0713  97  18  -8 0.01
Mon 03/23 14Z 0.39 0811  97  18  -8 0.01
Mon 03/23 15Z 0.30 0907  98  19  -8 0.01
Mon 03/23 16Z 0.24 0905  97  18  -8 0.00
Mon 03/23 17Z 0.16 0703  97  18  -8 0.00
Mon 03/23 18Z 0.14 0303  97  17  -8 0.01
Mon 03/23 19Z 0.09 3504  98  21  -8 0.01
Mon 03/23 20Z 0.09 3407  98  31  -8 0.01
Mon 03/23 21Z 0.16 3311  98  35  -8 0.01
Mon 03/23 22Z 0.22 3314  97  31  -9 0.01
Mon 03/23 23Z 0.22 3417  96  32  -9 0.01
Tue 03/24 00Z 0.19 3419  95  34  -9 0.01
Tue 03/24 01Z 0.21 3421  95  38 -10 0.01
Tue 03/24 02Z 0.25 3423  94  44 -10 0.01
Tue 03/24 03Z 0.24 3424  91  44 -10 0.00
Tue 03/24 04Z 0.22 3424  88  35 -11 0.00
Tue 03/24 05Z 0.27 3424  87  27 -11 0.00
Tue 03/24 06Z 0.33 3424  91  20 -11 0.00
Tue 03/24 07Z 0.39 3422  94  15 -12 0.01
Tue 03/24 08Z 0.36 3320  95   7 -12 0.01
Tue 03/24 09Z 0.31 3319  95   4 -12 0.01
Tue 03/24 10Z 0.32 3319  94   5 -12 0.01
Tue 03/24 11Z 0.28 3318  92   7 -13 0.01
Tue 03/24 12Z 0.30 3316  89  10 -13 0.00
Tue 03/24 13Z 0.28 3215  86  11 -13 0.00
Tue 03/24 14Z 0.22 3212  78  12 -12 0.00
Tue 03/24 15Z 0.28 3011  74  10 -12 0.00
Tue 03/24 16Z 0.36 2911  72   7 -11 0.00
Tue 03/24 17Z 0.32 2809  61   5 -10 0.00
Tue 03/24 18Z 0.31 2609  51   3  -9 0.00
Tue 03/24 19Z 0.28 2409  40   3  -8 0.00
Tue 03/24 20Z 0.39 2411  38   5  -8 0.00
Tue 03/24 21Z 0.64 2416  46   8  -8 0.00
Tue 03/24 22Z 0.90 2420  53  27  -8 0.00
Tue 03/24 23Z 0.97 2423  54  68  -8 0.00
Wed 03/25 00Z 2.14 2528  45  78  -8 0.00
Wed 03/25 01Z 4.85 2631  57  85  -9 0.00
Wed 03/25 02Z 4.80 2732  78  89 -10 0.01
Wed 03/25 03Z 1.54 2831  88  48 -10 0.01
Wed 03/25 04Z 1.38 2831  91  15 -10 0.01
Wed 03/25 05Z 1.29 2930  90  19 -11 0.01
Wed 03/25 06Z 1.05 2927  85  22 -10 0.00
Wed 03/25 07Z 0.76 2925  78   9  -9 0.00
Wed 03/25 08Z 0.65 2924  75   6  -9 0.00
Wed 03/25 09Z 0.76 2925  83   8  -9 0.00
Wed 03/25 10Z 0.78 2824  81  11  -9 0.01
Wed 03/25 11Z 0.64 2822  70  21  -8 0.00
Wed 03/25 12Z 0.49 2820  57  22  -7 0.00
Wed 03/25 13Z 0.37 2816  42  22  -5 0.00
Wed 03/25 14Z 0.32 2714  36  15  -5 0.00
Wed 03/25 15Z 0.31 2613  36  13  -4 0.00
Wed 03/25 16Z 0.30 2412  35  11  -4 0.00
Wed 03/25 17Z 0.34 2214  33   7  -4 0.00

Run total areal avg QPF for the greens is: 0.23 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