NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260519_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)
=== ===== === ==== ==== === === === ====
Tue 05/19 06Z 0.98 2431  70  51  18 0.00
Tue 05/19 07Z 1.00 2532  70  46  18 0.00
Tue 05/19 08Z 0.96 2531  70  59  18 0.00
Tue 05/19 09Z 0.93 2630  72  64  17 0.00
Tue 05/19 10Z 0.95 2628  77  44  16 0.00
Tue 05/19 11Z 0.86 2625  78  41  16 0.00
Tue 05/19 12Z 0.76 2623  83  27  16 0.00
Tue 05/19 13Z 0.77 2522  82  22  16 0.00
Tue 05/19 14Z 0.85 2521  86  40  15 0.02
Tue 05/19 15Z 2.13 2526  93  84  14 0.08
Tue 05/19 16Z 0.78 2524  80  62  15 0.04
Tue 05/19 17Z 0.90 2526  75  48  16 0.00
Tue 05/19 18Z 1.24 2525  74  38  15 0.00
Tue 05/19 19Z 4.06 2522  83  77  15 0.00
Tue 05/19 20Z 4.52 2522  87  70  15 0.00
Tue 05/19 21Z 3.04 2623  80  68  15 0.01
Tue 05/19 22Z 1.26 2623  81  54  15 0.00
Tue 05/19 23Z 1.26 2626  86  40  15 0.00
Wed 05/20 00Z 0.92 2628  80  45  16 0.00
Wed 05/20 01Z 0.92 2628  78  45  16 0.00
Wed 05/20 02Z 0.93 2630  77  47  17 0.00
Wed 05/20 03Z 1.05 2533  82  67  16 0.00
Wed 05/20 04Z 1.29 2535  83  69  16 0.00
Wed 05/20 05Z 1.48 2536  83  63  16 0.00
Wed 05/20 06Z 1.46 2439  78  52  16 0.00
Wed 05/20 07Z 1.34 2539  78  50  16 0.00
Wed 05/20 08Z 1.06 2535  81  54  16 0.00
Wed 05/20 09Z 1.02 2733  89  56  15 0.00
Wed 05/20 10Z 0.90 2731  87  51  15 0.00
Wed 05/20 11Z 0.81 2629  88  58  15 0.00
Wed 05/20 12Z 0.81 2728  92  52  14 0.00
Wed 05/20 13Z 0.82 2726  95  58  13 0.01
Wed 05/20 14Z 0.95 2725  96  48  12 0.03
Wed 05/20 15Z 1.04 2726  92  37  11 0.04
Wed 05/20 16Z 1.92 2724  76  31  11 0.01
Wed 05/20 17Z 9.55 2722  70  36  10 0.00
Wed 05/20 18Z 13.30 2821  68  34   9 0.00
Wed 05/20 19Z 11.93 2821  65  34   9 0.00
Wed 05/20 20Z 9.57 2920  64  32   9 0.00
Wed 05/20 21Z 5.95 2920  68  34   8 0.00
Wed 05/20 22Z 3.09 3021  75  33   7 0.00
Wed 05/20 23Z 1.01 3021  81  27   6 0.00
Thu 05/21 00Z 0.58 3023  85  20   5 0.00
Thu 05/21 01Z 0.56 3125  84  15   4 0.00
Thu 05/21 02Z 0.52 3125  79   8   3 0.00
Thu 05/21 03Z 0.48 3126  77   4   2 0.00
Thu 05/21 04Z 0.49 3227  78   3   1 0.00
Thu 05/21 05Z 0.39 3227  75   3   1 0.00
Thu 05/21 06Z 0.29 3226  75   3   0 0.00
Thu 05/21 07Z 0.23 3325  71   2   0 0.00
Thu 05/21 08Z 0.20 3326  69   2   0 0.00
Thu 05/21 09Z 0.18 3326  66   2   0 0.00
Thu 05/21 10Z 0.16 3326  63   2   0 0.00
Thu 05/21 11Z 0.12 3325  58   2   0 0.00
Thu 05/21 12Z 0.08 3322  55   2   0 0.00
Thu 05/21 13Z 0.08 3319  53   3   0 0.00
Thu 05/21 14Z 0.08 3317  52   5   0 0.00
Thu 05/21 15Z 0.09 3317  49   5   0 0.00
Thu 05/21 16Z 0.10 3316  49   5   0 0.00
Thu 05/21 17Z 0.19 3316  48   5   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.24 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