NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260120_1800
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 01/20 18Z 7.98 2515  82  64 -20 0.00
Tue 01/20 19Z 8.61 2519  83  62 -20 0.01
Tue 01/20 20Z 9.09 2621  81  61 -20 0.01
Tue 01/20 21Z 6.36 2621  78  61 -20 0.01
Tue 01/20 22Z 4.83 2723  77  51 -20 0.01
Tue 01/20 23Z 2.32 2624  80  40 -20 0.00
Wed 01/21 00Z 1.95 2626  82  35 -20 0.00
Wed 01/21 01Z 1.35 2627  77  34 -20 0.00
Wed 01/21 02Z 1.21 2628  79  36 -20 0.00
Wed 01/21 03Z 1.06 2628  80  39 -20 0.00
Wed 01/21 04Z 1.02 2629  80  36 -20 0.00
Wed 01/21 05Z 0.97 2629  82  36 -19 0.00
Wed 01/21 06Z 0.82 2628  80  35 -19 0.00
Wed 01/21 07Z 0.80 2529  79  30 -18 0.00
Wed 01/21 08Z 0.76 2629  73  20 -18 0.00
Wed 01/21 09Z 0.73 2630  72  12 -17 0.00
Wed 01/21 10Z 0.65 2628  70   8 -17 0.00
Wed 01/21 11Z 0.66 2528  69   9 -16 0.00
Wed 01/21 12Z 0.60 2527  65  10 -16 0.00
Wed 01/21 13Z 0.56 2526  58   9 -15 0.00
Wed 01/21 14Z 0.56 2526  53  13 -15 0.00
Wed 01/21 15Z 0.55 2425  50  40 -15 0.00
Wed 01/21 16Z 0.53 2423  49  75 -14 0.00
Wed 01/21 17Z 0.48 2321  47  91 -14 0.00
Wed 01/21 18Z 0.48 2222  43  95 -13 0.00
Wed 01/21 19Z 0.48 2223  37  88 -13 0.00
Wed 01/21 20Z 0.45 2123  51  84 -13 0.00
Wed 01/21 21Z 0.38 2026  64  90 -11 0.00
Wed 01/21 22Z 0.33 1928  76  88 -11 0.00
Wed 01/21 23Z 0.35 1933  88  89 -10 0.02
Thu 01/22 00Z 0.56 2038  90  90 -12 0.04
Thu 01/22 01Z 0.71 2042  92  89 -11 0.03
Thu 01/22 02Z 0.74 2143  93  86 -10 0.01
Thu 01/22 03Z 0.78 2240  95  88  -9 0.01
Thu 01/22 04Z 0.80 2237  95  91  -9 0.01
Thu 01/22 05Z 0.78 2335  96  77  -8 0.01
Thu 01/22 06Z 0.76 2333  95  54  -8 0.01
Thu 01/22 07Z 0.77 2332  94  36  -8 0.00
Thu 01/22 08Z 0.76 2331  94  30  -8 0.00
Thu 01/22 09Z 0.76 2429  94  34  -8 0.00
Thu 01/22 10Z 0.78 2329  94  45  -8 0.00
Thu 01/22 11Z 0.81 2329  95  52  -9 0.00
Thu 01/22 12Z 0.87 2329  95  67  -9 0.00
Thu 01/22 13Z 0.92 2330  95  77  -9 0.01
Thu 01/22 14Z 0.97 2331  94  68  -8 0.01
Thu 01/22 15Z 1.18 2433  95  62  -9 0.01
Thu 01/22 16Z 1.55 2432  91  48 -10 0.01
Thu 01/22 17Z 1.65 2428  88  38 -10 0.00
Thu 01/22 18Z 3.38 2426  92  45  -9 0.00
Thu 01/22 19Z 6.50 2429  93  21 -10 0.01
Thu 01/22 20Z 5.93 2430  90  30 -10 0.01
Thu 01/22 21Z 8.22 2532  82  22 -11 0.01
Thu 01/22 22Z 5.12 2433  83  27 -12 0.00
Thu 01/22 23Z 5.69 2436  85  26 -12 0.00
Fri 01/23 00Z 4.21 2535  87  27 -13 0.00
Fri 01/23 01Z 3.09 2534  85  23 -14 0.00
Fri 01/23 02Z 1.87 2534  77  23 -15 0.00
Fri 01/23 03Z 1.48 2534  78  24 -15 0.00
Fri 01/23 04Z 1.58 2632  80  25 -16 0.00
Fri 01/23 05Z 1.63 2630  84  24 -16 0.00

Run total areal avg QPF for the Central_Greens is: 0.25 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