NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260730_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)
=== ===== === ==== ==== === === === ====
Thu 07/30 12Z 0.25 0409  93  93  11 0.00
Thu 07/30 13Z 0.23 0310  89  92  11 0.01
Thu 07/30 14Z 0.21 0309  88  87  11 0.02
Thu 07/30 15Z 0.26 0309  90  84  11 0.02
Thu 07/30 16Z 0.19 0109  91  85  11 0.01
Thu 07/30 17Z 0.10 0009  92  83  12 0.02
Thu 07/30 18Z 0.33 3410  93  78  12 0.05
Thu 07/30 19Z 0.14 3513  91  81  12 0.09
Thu 07/30 20Z 0.09 3514  89  83  12 0.04
Thu 07/30 21Z 0.10 0014  90  80  12 0.04
Thu 07/30 22Z 0.12 0113  91  79  12 0.06
Thu 07/30 23Z 0.10 0111  93  81  12 0.04
Fri 07/31 00Z 0.10 0110  91  81  12 0.03
Fri 07/31 01Z 0.08 0110  87  79  12 0.03
Fri 07/31 02Z 0.07 0110  85  79  12 0.00
Fri 07/31 03Z 0.04 0010  85  79  12 0.00
Fri 07/31 04Z 0.04 0009  84  80  12 0.00
Fri 07/31 05Z 0.04 0008  83  82  12 0.00
Fri 07/31 06Z 0.05 3508  83  84  12 0.00
Fri 07/31 07Z 0.08 3408  84  84  12 0.00
Fri 07/31 08Z 0.08 3409  84  84  12 0.00
Fri 07/31 09Z 0.10 3409  85  81  12 0.00
Fri 07/31 10Z 0.12 3309  86  78  12 0.00
Fri 07/31 11Z 0.12 3309  87  76  12 0.00
Fri 07/31 12Z 0.16 3310  89  73  12 0.00
Fri 07/31 13Z 0.21 3210  91  72  11 0.01
Fri 07/31 14Z 0.25 3111  92  67  11 0.02
Fri 07/31 15Z 0.28 3110  92  59  11 0.01
Fri 07/31 16Z 0.29 3110  92  55  11 0.01
Fri 07/31 17Z 0.33 3110  90  48  12 0.01
Fri 07/31 18Z 0.37 3110  90  45  12 0.00
Fri 07/31 19Z 0.51 3110  90  51  12 0.00
Fri 07/31 20Z 0.46 3111  90  61  12 0.00
Fri 07/31 21Z 0.40 3111  88  61  12 0.01
Fri 07/31 22Z 0.34 3110  86  56  13 0.00
Fri 07/31 23Z 0.32 3109  88  55  13 0.00
Sat 08/01 00Z 0.38 3011  89  56  13 0.00
Sat 08/01 01Z 0.29 3109  90  52  13 0.01
Sat 08/01 02Z 0.25 3108  91  47  13 0.00
Sat 08/01 03Z 0.24 3007  91  45  13 0.00
Sat 08/01 04Z 0.25 2906  91  46  12 0.00
Sat 08/01 05Z 0.24 2906  88  44  13 0.00
Sat 08/01 06Z 0.25 2806  86  40  13 0.00
Sat 08/01 07Z 0.24 2906  84  32  13 0.00
Sat 08/01 08Z 0.17 2905  82  28  13 0.00
Sat 08/01 09Z 0.22 2805  82  24  13 0.00
Sat 08/01 10Z 0.19 2705  81  19  13 0.00
Sat 08/01 11Z 0.18 2704  78  16  13 0.00
Sat 08/01 12Z 0.16 2504  76  13  13 0.00
Sat 08/01 13Z 0.17 2505  75  14  13 0.00
Sat 08/01 14Z 0.13 2304  74  13  14 0.00
Sat 08/01 15Z 0.14 2203  75  14  14 0.00
Sat 08/01 16Z 0.18 2103  76  14  14 0.00
Sat 08/01 17Z 0.28 2003  76  16  14 0.00
Sat 08/01 18Z 0.28 2003  74  19  14 0.00
Sat 08/01 19Z 0.20 1904  74  25  15 0.00
Sat 08/01 20Z 0.18 1805  77  30  15 0.00
Sat 08/01 21Z 0.08 1706  79  32  15 0.00
Sat 08/01 22Z 0.09 1808  83  40  15 0.00
Sat 08/01 23Z 0.06 1810  85  54  15 0.00

Run total areal avg QPF for the greens is: 0.54 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