NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260602_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)
=== ===== === ==== ==== === === === ====
Tue 06/02 18Z 3.90 3313  48  34   7 0.00
Tue 06/02 19Z 4.66 3216  48  30   8 0.00
Tue 06/02 20Z 3.66 3317  46  29   8 0.00
Tue 06/02 21Z 2.40 3318  46  32   8 0.00
Tue 06/02 22Z 1.53 3419  49  36   8 0.00
Tue 06/02 23Z 0.60 3420  50  43   8 0.00
Wed 06/03 00Z 0.40 3421  49  46   8 0.00
Wed 06/03 01Z 0.31 3421  47  45   8 0.00
Wed 06/03 02Z 0.22 3520  46  40   9 0.00
Wed 06/03 03Z 0.16 3518  46  38   9 0.00
Wed 06/03 04Z 0.10 0017  46  35   9 0.00
Wed 06/03 05Z 0.15 0014  45  30   9 0.00
Wed 06/03 06Z 0.18 0112  44  26   9 0.00
Wed 06/03 07Z 0.14 0110  44  20   9 0.00
Wed 06/03 08Z 0.10 0108  43  15   9 0.00
Wed 06/03 09Z 0.04 3506  43  11   9 0.00
Wed 06/03 10Z 0.14 3306  44  12   9 0.00
Wed 06/03 11Z 0.20 3307  43  14   9 0.00
Wed 06/03 12Z 0.30 3109  44  15   9 0.00
Wed 06/03 13Z 0.38 3111  45  19   9 0.00
Wed 06/03 14Z 0.50 3113  46  25   9 0.00
Wed 06/03 15Z 1.00 3112  47  31   9 0.00
Wed 06/03 16Z 1.80 3212  48  36   9 0.00
Wed 06/03 17Z 2.29 3211  49  40  10 0.00
Wed 06/03 18Z 1.96 3209  50  42  10 0.00
Wed 06/03 19Z 1.75 3108  51  44  11 0.00
Wed 06/03 20Z 1.71 3008  51  45  11 0.00
Wed 06/03 21Z 1.30 2908  52  45  11 0.00
Wed 06/03 22Z 0.96 2809  55  48  11 0.00
Wed 06/03 23Z 0.73 2810  57  53  11 0.00
Thu 06/04 00Z 0.74 2712  59  55  12 0.00
Thu 06/04 01Z 0.80 2713  61  54  12 0.00
Thu 06/04 02Z 0.80 2813  59  50  11 0.00
Thu 06/04 03Z 0.74 3013  58  46  11 0.00
Thu 06/04 04Z 0.54 3012  61  41  11 0.00
Thu 06/04 05Z 0.46 3012  59  40  11 0.00
Thu 06/04 06Z 0.47 2911  57  37  12 0.00
Thu 06/04 07Z 0.47 2911  54  31  12 0.00
Thu 06/04 08Z 0.47 2910  52  28  12 0.00
Thu 06/04 09Z 0.45 2911  50  27  12 0.00
Thu 06/04 10Z 0.43 2910  49  28  12 0.00
Thu 06/04 11Z 0.51 2911  49  31  12 0.00
Thu 06/04 12Z 0.52 2911  51  32  12 0.00
Thu 06/04 13Z 0.53 2811  53  31  11 0.00
Thu 06/04 14Z 0.59 2810  56  31  12 0.00
Thu 06/04 15Z 0.96 2710  57  31  12 0.00
Thu 06/04 16Z 1.71 2611  56  30  12 0.00
Thu 06/04 17Z 3.12 2612  52  29  12 0.00
Thu 06/04 18Z 4.40 2613  55  27  12 0.00
Thu 06/04 19Z 6.69 2613  58  26  13 0.00
Thu 06/04 20Z 6.83 2714  55  29  13 0.00
Thu 06/04 21Z 3.49 2714  54  35  13 0.00
Thu 06/04 22Z 2.27 2715  57  30  13 0.00
Thu 06/04 23Z 2.00 2717  58  32  13 0.00
Fri 06/05 00Z 2.13 2719  60  29  13 0.00
Fri 06/05 01Z 1.68 2821  63  29  12 0.00
Fri 06/05 02Z 1.15 2922  65  31  12 0.00
Fri 06/05 03Z 0.96 2923  67  25  12 0.00
Fri 06/05 04Z 0.98 2924  71  26  11 0.00
Fri 06/05 05Z 0.95 3024  74  28  11 0.00

Run total areal avg QPF for the greens is: 0.00 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