NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260807_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)
=== ===== === ==== ==== === === === ====
Fri 08/07 18Z 0.45 2904  89  40  16 0.00
Fri 08/07 19Z 0.25 3003  87  44  16 0.04
Fri 08/07 20Z 0.13 3202  86  48  17 0.03
Fri 08/07 21Z 0.11 0001  86  49  17 0.01
Fri 08/07 22Z 0.08 0700  88  49  17 0.02
Fri 08/07 23Z 0.10 2501  88  51  17 0.04
Sat 08/08 00Z 0.10 2602  88  48  17 0.04
Sat 08/08 01Z 0.04 1701  87  46  17 0.02
Sat 08/08 02Z 0.06 1805  85  47  17 0.00
Sat 08/08 03Z 0.08 1806  85  52  17 0.00
Sat 08/08 04Z 0.10 1905  86  60  16 0.00
Sat 08/08 05Z 0.16 2105  90  74  16 0.00
Sat 08/08 06Z 0.14 2304  92  85  16 0.00
Sat 08/08 07Z 0.12 2303  92  92  16 0.05
Sat 08/08 08Z 0.12 2303  92  93  16 0.11
Sat 08/08 09Z 0.12 2304  91  88  16 0.03
Sat 08/08 10Z 0.14 2305  90  80  16 0.01
Sat 08/08 11Z 0.14 2304  89  76  16 0.00
Sat 08/08 12Z 0.13 2205  89  76  16 0.00
Sat 08/08 13Z 0.14 2205  90  78  16 0.00
Sat 08/08 14Z 0.17 2405  90  76  16 0.00
Sat 08/08 15Z 0.14 2304  88  68  16 0.00
Sat 08/08 16Z 0.21 2306  88  67  16 0.00
Sat 08/08 17Z 0.29 2408  87  68  16 0.00
Sat 08/08 18Z 0.39 2510  84  65  16 0.00
Sat 08/08 19Z 0.49 2511  84  59  16 0.00
Sat 08/08 20Z 0.58 2612  86  58  16 0.00
Sat 08/08 21Z 0.59 2513  90  55  16 0.01
Sat 08/08 22Z 0.56 2514  93  52  17 0.07
Sat 08/08 23Z 0.57 2615  92  42  16 0.11
Sun 08/09 00Z 0.58 2716  93  45  16 0.02
Sun 08/09 01Z 0.52 2715  93  48  16 0.01
Sun 08/09 02Z 0.41 2814  88  37  17 0.05
Sun 08/09 03Z 0.35 2813  84  42  17 0.01
Sun 08/09 04Z 0.32 2813  75  41  17 0.00
Sun 08/09 05Z 0.29 2912  68  31  17 0.00
Sun 08/09 06Z 0.28 2911  62  32  17 0.00
Sun 08/09 07Z 0.30 2811  64  45  17 0.00
Sun 08/09 08Z 0.32 2711  72  47  17 0.00
Sun 08/09 09Z 0.36 2712  83  42  16 0.00
Sun 08/09 10Z 0.37 2513  88  40  16 0.00
Sun 08/09 11Z 0.39 2514  90  36  16 0.00
Sun 08/09 12Z 0.38 2514  87  41  16 0.00
Sun 08/09 13Z 0.40 2514  87  28  16 0.00
Sun 08/09 14Z 0.43 2614  91  37  16 0.00
Sun 08/09 15Z 0.47 2514  92  58  16 0.00
Sun 08/09 16Z 0.51 2613  91  63  16 0.00
Sun 08/09 17Z 0.62 2512  93  70  15 0.00
Sun 08/09 18Z 0.61 2511  96  72  16 0.01
Sun 08/09 19Z 0.58 2513  93  67  16 0.22
Sun 08/09 20Z 0.53 2613  93  51  16 0.14
Sun 08/09 21Z 0.55 2714  92  23  16 0.11
Sun 08/09 22Z 0.52 2815  91  24  16 0.04
Sun 08/09 23Z 0.49 2916  87  19  16 0.03
Mon 08/10 00Z 0.41 3016  82  27  15 0.01
Mon 08/10 01Z 0.30 3116  74  32  15 0.01
Mon 08/10 02Z 0.25 3115  75  32  15 0.01
Mon 08/10 03Z 0.22 3115  75  25  15 0.01
Mon 08/10 04Z 0.19 3216  73  25  15 0.00
Mon 08/10 05Z 0.15 3216  67  28  15 0.00

Run total areal avg QPF for the Central_Greens is: 1.27 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