NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261028_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)
=== ===== === ==== ==== === === === ====
Wed 10/28 18Z 0.24 2511  39  80   6 0.00
Wed 10/28 19Z 0.22 2510  37  86   7 0.00
Wed 10/28 20Z 0.23 2510  38  88   7 0.00
Wed 10/28 21Z 0.24 2412  41  82   7 0.00
Wed 10/28 22Z 0.28 2414  45  84   8 0.00
Wed 10/28 23Z 0.32 2514  51  84   8 0.00
Thu 10/29 00Z 0.35 2515  56  87   8 0.00
Thu 10/29 01Z 0.36 2516  60  83   8 0.00
Thu 10/29 02Z 0.40 2517  64  84   8 0.00
Thu 10/29 03Z 0.43 2517  68  69   8 0.00
Thu 10/29 04Z 0.44 2518  70  59   8 0.00
Thu 10/29 05Z 0.43 2418  73  48   8 0.00
Thu 10/29 06Z 0.43 2419  77  35   8 0.00
Thu 10/29 07Z 0.43 2419  79  25   8 0.00
Thu 10/29 08Z 0.43 2420  84  22   8 0.00
Thu 10/29 09Z 0.44 2420  86  20   8 0.00
Thu 10/29 10Z 0.47 2421  88  23   7 0.01
Thu 10/29 11Z 0.49 2421  90  28   7 0.01
Thu 10/29 12Z 0.54 2422  92  33   7 0.01
Thu 10/29 13Z 0.57 2422  91  40   7 0.01
Thu 10/29 14Z 0.59 2423  91  44   7 0.01
Thu 10/29 15Z 0.60 2423  87  50   7 0.01
Thu 10/29 16Z 0.59 2423  87  63   8 0.00
Thu 10/29 17Z 0.61 2424  88  60   8 0.00
Thu 10/29 18Z 0.64 2425  86  57   8 0.00
Thu 10/29 19Z 0.70 2425  88  49   8 0.00
Thu 10/29 20Z 0.75 2427  89  46   8 0.00
Thu 10/29 21Z 0.78 2529  84  49   8 0.00
Thu 10/29 22Z 0.79 2531  79  67   9 0.00
Thu 10/29 23Z 0.76 2432  80  83  10 0.00
Fri 10/30 00Z 0.82 2434  82  89   9 0.00
Fri 10/30 01Z 0.87 2435  85  90   9 0.01
Fri 10/30 02Z 0.92 2536  90  93   9 0.02
Fri 10/30 03Z 0.96 2536  94  85   8 0.05
Fri 10/30 04Z 0.96 2535  97  77   8 0.06
Fri 10/30 05Z 0.99 2633  97  49   8 0.04
Fri 10/30 06Z 0.97 2731  95  31   7 0.03
Fri 10/30 07Z 0.97 2728  91  12   6 0.02
Fri 10/30 08Z 0.92 2727  86  12   6 0.02
Fri 10/30 09Z 0.91 2727  81   8   5 0.02
Fri 10/30 10Z 0.91 2727  80   7   5 0.01
Fri 10/30 11Z 0.84 2727  75   7   4 0.01
Fri 10/30 12Z 0.86 2827  76   6   3 0.01
Fri 10/30 13Z 0.81 2827  81   6   2 0.01
Fri 10/30 14Z 0.76 2925  85  10   2 0.02
Fri 10/30 15Z 0.82 2924  89  18   1 0.02
Fri 10/30 16Z 0.96 2923  92  18   0 0.01
Fri 10/30 17Z 1.11 2923  94  22   0 0.01
Fri 10/30 18Z 1.15 2923  94  24   0 0.02
Fri 10/30 19Z 1.18 2925  95  31   0 0.02
Fri 10/30 20Z 1.28 2926  96  35  -1 0.03
Fri 10/30 21Z 1.19 3027  96  38  -1 0.03
Fri 10/30 22Z 1.26 3030  97  40  -2 0.02
Fri 10/30 23Z 1.29 3032  97  37  -2 0.02
Sat 10/31 00Z 1.08 3133  98  32  -3 0.02
Sat 10/31 01Z 1.03 3134  97  33  -4 0.01
Sat 10/31 02Z 1.05 3233  97  36  -5 0.01
Sat 10/31 03Z 0.85 3231  96  36  -6 0.01
Sat 10/31 04Z 0.65 3230  93  26  -6 0.01
Sat 10/31 05Z 0.60 3231  90  16  -6 0.00

Run total areal avg QPF for the greens is: 0.63 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