NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260711_1200
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)
=== ===== === ==== ==== === === === ====
Sat 07/11 12Z 0.16 3309  71  29  11 0.00
Sat 07/11 13Z 0.19 3310  70  33  11 0.00
Sat 07/11 14Z 0.19 3408  69  34  11 0.00
Sat 07/11 15Z 0.42 3408  68  31  11 0.00
Sat 07/11 16Z 0.88 3309  68  32  11 0.00
Sat 07/11 17Z 1.34 3309  66  29  11 0.00
Sat 07/11 18Z 1.05 3409  62  25  11 0.00
Sat 07/11 19Z 0.79 3409  60  21  12 0.00
Sat 07/11 20Z 0.53 3509  59  17  12 0.00
Sat 07/11 21Z 0.26 3509  60  12  12 0.00
Sat 07/11 22Z 0.21 0009  61  10  12 0.00
Sat 07/11 23Z 0.25 0110  62  10  11 0.00
Sun 07/12 00Z 0.38 0110  65  10  11 0.00
Sun 07/12 01Z 0.46 0211  66  11  11 0.00
Sun 07/12 02Z 0.63 0312  68  10  11 0.00
Sun 07/12 03Z 0.72 0411  67  10  10 0.00
Sun 07/12 04Z 0.76 0411  67  11  10 0.00
Sun 07/12 05Z 0.71 0410  66  12  10 0.00
Sun 07/12 06Z 0.61 0410  66  11  10 0.00
Sun 07/12 07Z 0.49 0409  65  10  10 0.00
Sun 07/12 08Z 0.36 0408  66   9  10 0.00
Sun 07/12 09Z 0.31 0407  66   9  10 0.00
Sun 07/12 10Z 0.27 0306  67   8   9 0.00
Sun 07/12 11Z 0.28 0307  67   8   9 0.00
Sun 07/12 12Z 0.25 0306  67   8   9 0.00
Sun 07/12 13Z 0.32 0205  69   7   9 0.00
Sun 07/12 14Z 0.75 0204  72   7   9 0.00
Sun 07/12 15Z 0.43 3502  73   8  10 0.00
Sun 07/12 16Z 0.49 3402  74   7  10 0.00
Sun 07/12 17Z 0.46 3402  75   7  10 0.00
Sun 07/12 18Z 0.70 3103  77   7  11 0.00
Sun 07/12 19Z 0.90 3103  78  10  11 0.00
Sun 07/12 20Z 0.78 3103  77   9  11 0.00
Sun 07/12 21Z 0.69 3003  75   8  11 0.00
Sun 07/12 22Z 0.36 2803  72   9  12 0.00
Sun 07/12 23Z 0.19 2502  66   5  12 0.00
Mon 07/13 00Z 0.13 2203  63   4  12 0.00
Mon 07/13 01Z 0.25 2205  64   4  12 0.00
Mon 07/13 02Z 0.46 2406  67   5  11 0.00
Mon 07/13 03Z 0.53 2308  70   7  11 0.00
Mon 07/13 04Z 0.61 2310  72   8  11 0.00
Mon 07/13 05Z 0.71 2411  72   9  11 0.00
Mon 07/13 06Z 0.92 2514  74  12  11 0.00
Mon 07/13 07Z 0.91 2515  74  15  11 0.00
Mon 07/13 08Z 0.97 2517  72  20  11 0.00
Mon 07/13 09Z 0.98 2517  68  24  11 0.00
Mon 07/13 10Z 0.86 2618  66  33  12 0.00
Mon 07/13 11Z 0.73 2617  65  38  12 0.00
Mon 07/13 12Z 0.64 2616  63  39  12 0.00
Mon 07/13 13Z 0.56 2615  62  43  13 0.00
Mon 07/13 14Z 0.59 2516  59  50  13 0.00
Mon 07/13 15Z 0.61 2615  55  56  13 0.00
Mon 07/13 16Z 0.65 2614  58  67  13 0.00
Mon 07/13 17Z 0.80 2614  69  78  13 0.00
Mon 07/13 18Z 0.74 2615  74  87  14 0.00
Mon 07/13 19Z 1.49 2516  78  79  14 0.00
Mon 07/13 20Z 1.54 2517  85  79  13 0.01
Mon 07/13 21Z 1.05 2619  86  73  14 0.02
Mon 07/13 22Z 1.14 2720  86  71  14 0.01
Mon 07/13 23Z 1.25 2820  85  68  14 0.01

Run total areal avg QPF for the 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