NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260517_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)
=== ===== === ==== ==== === === === ====
Sun 05/17 18Z 8.01 2813  76  56  10 0.00
Sun 05/17 19Z 5.81 2913  75  49  10 0.01
Sun 05/17 20Z 3.09 3018  76  41  10 0.04
Sun 05/17 21Z 1.44 3018  75  33  10 0.01
Sun 05/17 22Z 1.14 3117  72  26  10 0.00
Sun 05/17 23Z 0.66 3117  69  24  10 0.00
Mon 05/18 00Z 0.50 3216  66  20   9 0.00
Mon 05/18 01Z 0.39 3214  64  18   9 0.00
Mon 05/18 02Z 0.38 3012  65  17   9 0.00
Mon 05/18 03Z 0.37 2911  66  17  10 0.00
Mon 05/18 04Z 0.33 2810  67  21  10 0.00
Mon 05/18 05Z 0.29 2809  67  31  10 0.00
Mon 05/18 06Z 0.26 2709  65  40  11 0.00
Mon 05/18 07Z 0.26 2709  62  48  11 0.00
Mon 05/18 08Z 0.26 2609  64  43  11 0.00
Mon 05/18 09Z 0.26 2409  68  44  12 0.00
Mon 05/18 10Z 0.21 2209  73  66  12 0.00
Mon 05/18 11Z 0.15 2012  76  85  12 0.00
Mon 05/18 12Z 0.29 2118  86  91  10 0.04
Mon 05/18 13Z 0.15 2018  85  65  12 0.18
Mon 05/18 14Z 0.23 2024  92  60  12 0.01
Mon 05/18 15Z 0.32 2127  96  39  12 0.01
Mon 05/18 16Z 0.41 2126  96  36  12 0.01
Mon 05/18 17Z 0.47 2223  93  36  12 0.01
Mon 05/18 18Z 0.55 2221  90  33  13 0.00
Mon 05/18 19Z 0.60 2222  93  28  13 0.00
Mon 05/18 20Z 0.68 2223  94  21  13 0.01
Mon 05/18 21Z 0.73 2323  94  20  14 0.01
Mon 05/18 22Z 0.75 2323  93  23  14 0.01
Mon 05/18 23Z 0.75 2323  91  27  15 0.01
Tue 05/19 00Z 0.80 2324  91  25  15 0.00
Tue 05/19 01Z 0.84 2326  90  23  15 0.00
Tue 05/19 02Z 0.87 2327  86  21  16 0.00
Tue 05/19 03Z 0.88 2429  81  16  16 0.00
Tue 05/19 04Z 1.03 2433  82  26  16 0.00
Tue 05/19 05Z 1.21 2436  83  33  16 0.00
Tue 05/19 06Z 1.14 2437  78  35  17 0.00
Tue 05/19 07Z 1.28 2539  79  37  17 0.00
Tue 05/19 08Z 1.22 2636  85  47  15 0.02
Tue 05/19 09Z 1.17 2632  86  44  15 0.01
Tue 05/19 10Z 1.22 2632  88  39  14 0.00
Tue 05/19 11Z 0.98 2531  79  47  15 0.00
Tue 05/19 12Z 0.97 2530  85  41  14 0.00
Tue 05/19 13Z 1.03 2530  90  67  14 0.00
Tue 05/19 14Z 1.09 2629  96  81  13 0.02
Tue 05/19 15Z 1.18 2628  97  75  13 0.04
Tue 05/19 16Z 0.99 2724  96  73  13 0.03
Tue 05/19 17Z 0.82 2720  89  54  14 0.01
Tue 05/19 18Z 0.70 2717  82  52  15 0.00
Tue 05/19 19Z 0.74 2616  77  52  15 0.00
Tue 05/19 20Z 0.80 2517  73  51  16 0.00
Tue 05/19 21Z 0.95 2518  74  53  16 0.00
Tue 05/19 22Z 0.96 2420  76  49  16 0.00
Tue 05/19 23Z 1.20 2422  82  51  16 0.00
Wed 05/20 00Z 1.03 2422  82  56  16 0.00
Wed 05/20 01Z 0.96 2327  85  70  16 0.00
Wed 05/20 02Z 0.99 2332  83  79  17 0.00
Wed 05/20 03Z 0.89 2432  70  78  17 0.04
Wed 05/20 04Z 1.23 2439  79  76  17 0.00
Wed 05/20 05Z 1.30 2441  81  76  16 0.00

Run total areal avg QPF for the greens is: 0.53 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