NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260830_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)
=== ===== === ==== ==== === === === ====
Sun 08/30 18Z 1.00 2720  89  84  11 0.00
Sun 08/30 19Z 1.12 2718  86  86  11 0.00
Sun 08/30 20Z 0.92 2617  87  86  11 0.01
Sun 08/30 21Z 0.79 2618  86  82  11 0.05
Sun 08/30 22Z 0.84 2721  82  76  11 0.06
Sun 08/30 23Z 0.97 2823  83  73  11 0.03
Mon 08/31 00Z 1.04 2925  83  59  11 0.00
Mon 08/31 01Z 0.97 3025  84  43  11 0.00
Mon 08/31 02Z 0.71 3124  87  44  10 0.03
Mon 08/31 03Z 0.47 3222  86  51  10 0.02
Mon 08/31 04Z 0.27 3419  81  45  10 0.02
Mon 08/31 05Z 0.13 3516  75  21  10 0.00
Mon 08/31 06Z 0.06 3514  68   6  10 0.00
Mon 08/31 07Z 0.03 3512  61   4  10 0.00
Mon 08/31 08Z 0.06 3410  56   3  10 0.00
Mon 08/31 09Z 0.07 3409  52   4  10 0.00
Mon 08/31 10Z 0.10 3309  47   3  10 0.00
Mon 08/31 11Z 0.12 3309  44   3  11 0.00
Mon 08/31 12Z 0.12 3209  41   3  11 0.00
Mon 08/31 13Z 0.12 3209  40   3  11 0.00
Mon 08/31 14Z 0.10 3207  43   3  11 0.00
Mon 08/31 15Z 0.08 3204  47   3  11 0.00
Mon 08/31 16Z 0.09 3003  54   3  11 0.00
Mon 08/31 17Z 0.18 2804  59   6  10 0.00
Mon 08/31 18Z 0.23 2704  59  10  10 0.00
Mon 08/31 19Z 0.24 2603  56  16  11 0.00
Mon 08/31 20Z 0.20 2503  56  20  11 0.00
Mon 08/31 21Z 0.27 2604  56  26  11 0.00
Mon 08/31 22Z 0.17 2504  55  29  11 0.00
Mon 08/31 23Z 0.16 2404  57  31  11 0.00
Tue 09/01 00Z 0.19 2405  59  36  11 0.00
Tue 09/01 01Z 0.20 2405  61  40  11 0.00
Tue 09/01 02Z 0.19 2405  63  42  11 0.00
Tue 09/01 03Z 0.17 2405  67  42  11 0.00
Tue 09/01 04Z 0.12 2304  70  40  11 0.00
Tue 09/01 05Z 0.11 2204  74  44  11 0.00
Tue 09/01 06Z 0.09 2204  76  52  11 0.00
Tue 09/01 07Z 0.05 2004  77  63  11 0.00
Tue 09/01 08Z 0.05 1703  77  73  12 0.00
Tue 09/01 09Z 0.07 1504  78  76  12 0.00
Tue 09/01 10Z 0.10 1406  82  77  12 0.03
Tue 09/01 11Z 0.11 1507  87  82  11 0.08
Tue 09/01 12Z 0.19 1409  89  87  11 0.05
Tue 09/01 13Z 0.26 1313  91  83  11 0.11
Tue 09/01 14Z 0.27 1415  92  80  11 0.14
Tue 09/01 15Z 0.28 1418  92  83  12 0.07
Tue 09/01 16Z 0.32 1419  93  81  12 0.01
Tue 09/01 17Z 0.32 1419  94  79  12 0.01
Tue 09/01 18Z 0.28 1419  95  77  12 0.01
Tue 09/01 19Z 0.30 1418  96  77  12 0.01
Tue 09/01 20Z 0.31 1417  96  78  11 0.02
Tue 09/01 21Z 0.31 1420  96  79  11 0.01
Tue 09/01 22Z 0.28 1522  96  79  11 0.01
Tue 09/01 23Z 0.30 1424  95  72  12 0.01
Wed 09/02 00Z 0.29 1525  95  76  12 0.01
Wed 09/02 01Z 0.28 1526  94  83  11 0.01
Wed 09/02 02Z 0.29 1526  94  88  12 0.01
Wed 09/02 03Z 0.28 1525  94  88  12 0.01
Wed 09/02 04Z 0.24 1524  93  88  12 0.01
Wed 09/02 05Z 0.24 1524  91  88  12 0.02

Run total areal avg QPF for the 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