NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260901_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)
=== ===== === ==== ==== === === === ====
Tue 09/01 18Z 0.07 1605  99  81  11 0.00
Tue 09/01 19Z 0.10 1405  97  79  11 0.01
Wed 09/02 00Z 0.24 1316  92  46  12 0.01
Wed 09/02 01Z 0.24 1417  91  57  11 0.01
Wed 09/02 02Z 0.25 1417  92  68  11 0.00
Wed 09/02 03Z 0.20 1417  91  75  11 0.00
Wed 09/02 04Z 0.16 1518  91  76  11 0.00
Wed 09/02 05Z 0.13 1517  91  77  11 0.00
Wed 09/02 06Z 0.10 1515  91  73  11 0.01
Wed 09/02 07Z 0.12 1515  89  63  11 0.00
Wed 09/02 08Z 0.10 1514  87  55  11 0.00
Wed 09/02 09Z 0.07 1615  85  56  11 0.00
Wed 09/02 10Z 0.06 1616  83  56  11 0.00
Wed 09/02 11Z 0.04 1616  83  57  11 0.00
Wed 09/02 12Z 0.04 1616  83  52  11 0.00
Wed 09/02 13Z 0.05 1615  83  40  11 0.00
Wed 09/02 14Z 0.04 1715  81  41  11 0.00
Wed 09/02 15Z 0.05 1616  80  45  11 0.00
Wed 09/02 16Z 0.07 1617  80  44  11 0.00
Wed 09/02 17Z 0.08 1617  77  36  11 0.00
Wed 09/02 18Z 0.09 1617  74  25  11 0.00
Wed 09/02 19Z 0.11 1618  74  23  12 0.00
Wed 09/02 20Z 0.11 1618  79  30  12 0.00
Wed 09/02 21Z 0.14 1618  84  43  11 0.00
Wed 09/02 22Z 0.11 1620  84  52  11 0.00
Wed 09/02 23Z 0.08 1722  80  66  11 0.00
Thu 09/03 00Z 0.06 1722  78  75  12 0.00
Thu 09/03 01Z 0.06 1723  81  83  13 0.00
Thu 09/03 02Z 0.11 1824  86  70  13 0.00
Thu 09/03 03Z 0.19 1825  91  61  13 0.00
Thu 09/03 04Z 0.26 1926  94  49  13 0.00
Thu 09/03 05Z 0.21 1924  95  62  14 0.00
Thu 09/03 06Z 0.29 1926  96  79  13 0.00
Thu 09/03 07Z 0.20 1924  95  80  14 0.00
Thu 09/03 08Z 0.34 1930  98  92  13 0.00
Thu 09/03 09Z 0.36 2030  97  96  13 0.01
Thu 09/03 10Z 0.32 1930  94  99  14 0.01
Thu 09/03 11Z 0.36 2030  97  94  14 0.04
Thu 09/03 12Z 0.43 2035  99  97  14 0.07
Thu 09/03 13Z 0.67 2235  99  91  14 0.17
Thu 09/03 14Z 0.77 2334  99  88  14 0.15
Thu 09/03 15Z 0.74 2428  99  86  14 0.23
Thu 09/03 16Z 0.68 2523  99  77  14 0.46
Thu 09/03 17Z 0.61 2618  98  72  14 0.22
Thu 09/03 18Z 0.59 2616  99  82  14 0.13
Thu 09/03 19Z 0.50 2713  99  79  14 0.10
Thu 09/03 20Z 0.48 2712  98  82  14 0.07
Thu 09/03 21Z 0.49 2916  97  69  14 0.03
Thu 09/03 22Z 0.38 3116  96  57  13 0.03
Thu 09/03 23Z 0.27 3215  95  39  13 0.03
Fri 09/04 00Z 0.20 3214  92  18  12 0.08
Fri 09/04 01Z 0.24 3215  88  18  12 0.13
Fri 09/04 02Z 0.30 3116  85  37  12 0.02
Fri 09/04 03Z 0.40 3017  88  44  12 0.01
Fri 09/04 04Z 0.38 3016  88  48  12 0.01
Fri 09/04 05Z 0.36 3017  92  27  12 0.00

Run total areal avg QPF for the Central_Greens is: 2.04 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