NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260526_1200
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 05/26 12Z 0.30 3115  80  31  10 0.00
Tue 05/26 13Z 0.31 3013  78  43  11 0.00
Tue 05/26 14Z 0.40 2913  78  51  11 0.00
Tue 05/26 15Z 0.44 2812  75  52  11 0.00
Tue 05/26 16Z 0.54 2712  71  54  12 0.00
Tue 05/26 17Z 0.69 2612  72  56  12 0.00
Tue 05/26 18Z 1.14 2613  75  42  12 0.00
Tue 05/26 19Z 1.96 2515  78  33  13 0.00
Tue 05/26 20Z 2.04 2417  81  25  13 0.01
Tue 05/26 21Z 2.55 2420  80  31  13 0.00
Tue 05/26 22Z 2.61 2422  71  35  13 0.00
Tue 05/26 23Z 1.98 2526  65  41  13 0.00
Wed 05/27 00Z 1.85 2431  64  44  13 0.00
Wed 05/27 01Z 1.73 2436  72  45  13 0.00
Wed 05/27 02Z 1.38 2536  67  55  13 0.00
Wed 05/27 03Z 1.39 2537  66  61  13 0.00
Wed 05/27 04Z 1.38 2537  66  63  13 0.00
Wed 05/27 05Z 1.29 2637  66  60  13 0.00
Wed 05/27 06Z 1.22 2736  68  55  13 0.00
Wed 05/27 07Z 1.10 2833  70  56  12 0.00
Wed 05/27 08Z 1.01 2830  76  56  12 0.00
Wed 05/27 09Z 0.88 2826  84  55  11 0.00
Wed 05/27 10Z 0.75 2824  87  58  11 0.00
Wed 05/27 11Z 0.62 2821  87  57  11 0.00
Wed 05/27 12Z 0.54 2818  88  50  11 0.00
Wed 05/27 13Z 0.46 2916  89  42  10 0.00
Wed 05/27 14Z 0.46 3015  89  39   9 0.00
Wed 05/27 15Z 0.82 3014  89  34   9 0.00
Wed 05/27 16Z 2.45 3014  89  24   9 0.00
Wed 05/27 17Z 2.16 3012  88  22   9 0.00
Wed 05/27 18Z 1.71 3013  86  13   9 0.01
Wed 05/27 19Z 2.16 3114  81  15   9 0.00
Wed 05/27 20Z 1.59 3216  76  18   9 0.01
Wed 05/27 21Z 1.46 3216  70  19   9 0.00
Wed 05/27 22Z 0.82 3316  69  20   8 0.00
Wed 05/27 23Z 0.34 3317  73  22   8 0.00
Thu 05/28 00Z 0.22 3319  77  24   7 0.00
Thu 05/28 01Z 0.15 3420  80  29   7 0.00
Thu 05/28 02Z 0.10 3421  81  31   7 0.00
Thu 05/28 03Z 0.12 3421  86  32   6 0.00
Thu 05/28 04Z 0.17 3321  90  42   6 0.00
Thu 05/28 05Z 0.14 3420  91  43   6 0.00
Thu 05/28 06Z 0.09 3418  91  38   5 0.00
Thu 05/28 07Z 0.05 3517  89  53   5 0.00
Thu 05/28 08Z 0.04 3417  87  61   5 0.00
Thu 05/28 09Z 0.07 3417  86  70   4 0.00
Thu 05/28 10Z 0.07 3418  88  53   4 0.00
Thu 05/28 11Z 0.06 3418  93  50   3 0.00
Thu 05/28 12Z 0.04 3418  95  53   3 0.00
Thu 05/28 13Z 0.05 3418  97  58   2 0.00
Thu 05/28 14Z 0.10 3420  95  59   2 0.00
Thu 05/28 15Z 0.08 3421  89  54   2 0.00
Thu 05/28 16Z 0.20 3420  88  52   2 0.00
Thu 05/28 17Z 0.89 3419  88  55   2 0.00
Thu 05/28 18Z 1.30 3419  86  58   2 0.00
Thu 05/28 19Z 1.09 3419  86  57   2 0.00
Thu 05/28 20Z 1.07 3319  86  60   2 0.00
Thu 05/28 21Z 0.80 3320  87  66   2 0.01
Thu 05/28 22Z 0.25 3423  91  79   2 0.01
Thu 05/28 23Z 0.08 3423  88  73   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.05 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