NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261001_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)
=== ===== === ==== ==== === === === ====
Thu 10/01 18Z 0.71 2420  99  96  10 0.00
Thu 10/01 19Z 0.78 2423  98  93  11 0.03
Thu 10/01 20Z 0.77 2524  94  89  12 0.01
Thu 10/01 21Z 0.79 2525  93  86  12 0.00
Thu 10/01 22Z 0.74 2426  96  90  13 0.01
Thu 10/01 23Z 0.70 2424  95  79  13 0.02
Fri 10/02 00Z 0.84 2430  98  85  14 0.03
Fri 10/02 01Z 0.88 2531  98  80  14 0.05
Fri 10/02 02Z 0.91 2531  97  73  14 0.04
Fri 10/02 03Z 0.88 2531  96  51  15 0.03
Fri 10/02 04Z 0.90 2532  95  56  15 0.02
Fri 10/02 05Z 0.93 2434  94  50  15 0.02
Fri 10/02 06Z 1.01 2437  94  64  15 0.02
Fri 10/02 07Z 1.02 2437  92  69  15 0.02
Fri 10/02 08Z 1.03 2438  91  75  15 0.01
Fri 10/02 09Z 1.06 2536  92  75  15 0.01
Fri 10/02 10Z 1.04 2535  92  78  15 0.01
Fri 10/02 11Z 1.01 2533  94  76  15 0.04
Fri 10/02 12Z 0.98 2531  96  72  14 0.07
Fri 10/02 13Z 0.92 2527  95  89  14 0.09
Fri 10/02 14Z 0.78 2621  96  90  13 0.07
Fri 10/02 15Z 0.69 2719  97  94  13 0.07
Fri 10/02 16Z 0.62 2819  97  96  12 0.05
Fri 10/02 17Z 0.52 2817  97  94  12 0.03
Fri 10/02 18Z 0.44 2915  97  92  12 0.04
Fri 10/02 19Z 0.46 2916  95  87  11 0.03
Fri 10/02 20Z 0.47 2918  95  74  11 0.02
Fri 10/02 21Z 0.38 3019  97  48  10 0.01
Fri 10/02 22Z 0.37 3122  91  20  10 0.01
Fri 10/02 23Z 0.37 3124  73   5   9 0.00
Sat 10/03 00Z 0.29 3226  57   2   8 0.00
Sat 10/03 01Z 0.17 3326  50   2   7 0.00
Sat 10/03 02Z 0.12 3424  55   2   6 0.00
Sat 10/03 03Z 0.17 3323  69   2   5 0.00
Sat 10/03 04Z 0.21 3324  79   3   5 0.00
Sat 10/03 05Z 0.25 3323  81   6   4 0.00
Sat 10/03 06Z 0.23 3323  83   5   4 0.00
Sat 10/03 07Z 0.18 3321  84   1   4 0.00
Sat 10/03 08Z 0.13 3320  83   3   4 0.00
Sat 10/03 09Z 0.08 3419  80   4   3 0.00
Sat 10/03 10Z 0.06 3417  80   4   3 0.00
Sat 10/03 11Z 0.05 3417  78   3   3 0.00
Sat 10/03 12Z 0.03 3417  75   2   3 0.00
Sat 10/03 13Z 0.02 3417  72   2   4 0.00
Sat 10/03 14Z 0.02 3416  70   2   4 0.00
Sat 10/03 15Z 0.03 3415  69   2   4 0.00
Sat 10/03 16Z 0.04 3414  67   2   4 0.00
Sat 10/03 17Z 0.04 3412  67   3   4 0.00
Sat 10/03 18Z 0.04 3410  70   4   3 0.00
Sat 10/03 19Z 0.06 3409  70   5   3 0.00
Sat 10/03 20Z 0.04 3408  70   6   3 0.00
Sat 10/03 21Z 0.03 3407  69   5   3 0.00
Sat 10/03 22Z 0.02 3506  63   5   4 0.00
Sat 10/03 23Z 0.05 0005  57   5   4 0.00
Sun 10/04 00Z 0.07 0204  51   4   4 0.00
Sun 10/04 01Z 0.07 0402  48   5   4 0.00
Sun 10/04 02Z 0.06 0902  46   5   5 0.00
Sun 10/04 03Z 0.05 1202  44   5   5 0.00
Sun 10/04 04Z 0.03 1503  46   4   5 0.00
Sun 10/04 05Z 0.02 1606  50   3   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.86 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