Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260617_0600
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)
=== ===== === ==== ==== === === === ====
Wed 06/17 06Z 0.43 2311  76  46   9 0.00
Wed 06/17 07Z 0.48 2211  76  49   9 0.00
Wed 06/17 08Z 0.41 2210  74  51   9 0.00
Wed 06/17 09Z 0.34 2109  70  52   9 0.00
Wed 06/17 10Z 0.32 2109  69  53   9 0.00
Wed 06/17 11Z 0.29 2109  68  50   9 0.00
Wed 06/17 12Z 0.22 2007  67  51   9 0.00
Wed 06/17 13Z 0.23 1907  67  59   9 0.00
Wed 06/17 14Z 0.36 1807  68  71   9 0.00
Wed 06/17 15Z 0.50 1707  68  76  10 0.00
Wed 06/17 16Z 0.77 1808  72  70  10 0.02
Wed 06/17 17Z 0.92 1809  72  55  10 0.02
Wed 06/17 18Z 0.70 1809  74  60  10 0.02
Wed 06/17 19Z 1.52 1910  73  67  10 0.03
Wed 06/17 20Z 0.66 1808  72  78  10 0.01
Wed 06/17 21Z 0.28 1710  70  76  11 0.00
Wed 06/17 22Z 0.73 1811  70  73  11 0.00
Wed 06/17 23Z 0.49 1813  73  70  11 0.00
Thu 06/18 00Z 0.38 1815  75  59  11 0.00
Thu 06/18 01Z 0.60 2018  78  50  11 0.00
Thu 06/18 02Z 0.53 2019  85  39  11 0.00
Thu 06/18 03Z 0.51 2021  88  33  11 0.00
Thu 06/18 04Z 0.42 2018  87  67  11 0.00
Thu 06/18 05Z 0.38 2018  83  51  11 0.00
Thu 06/18 06Z 0.38 2020  83  54  11 0.00
Thu 06/18 07Z 0.43 2022  88  72  11 0.00
Thu 06/18 08Z 0.31 1923  89  91  11 0.01
Thu 06/18 09Z 0.30 1926  91  76  11 0.03
Thu 06/18 10Z 0.25 1827  90  68  12 0.02
Thu 06/18 11Z 0.29 1929  93  91  12 0.01
Thu 06/18 12Z 0.24 1832  84  92  13 0.01
Thu 06/18 13Z 0.20 1835  87  73  13 0.02
Thu 06/18 14Z 0.13 1741  87  83  14 0.01
Thu 06/18 15Z 0.24 1843  95  95  13 0.05
Thu 06/18 16Z 0.33 1841  96  98  13 0.10
Thu 06/18 17Z 0.38 1838  98  92  13 0.29
Thu 06/18 18Z 0.46 1935  97  90  14 0.13
Thu 06/18 19Z 0.54 1932  95  65  14 0.06
Thu 06/18 20Z 0.76 2030  95  63  14 0.05
Thu 06/18 21Z 0.98 2323  96  87  14 0.11
Thu 06/18 22Z 1.10 2526  83  32  14 0.15
Thu 06/18 23Z 1.48 2426  89  42  12 0.00
Fri 06/19 00Z 1.73 2429  93  57  12 0.01
Fri 06/19 01Z 1.96 2533  91  63  10 0.05
Fri 06/19 02Z 1.73 2533  90  64   9 0.02
Fri 06/19 03Z 1.49 2532  95  65   8 0.01
Fri 06/19 04Z 1.33 2532  96  68   7 0.02
Fri 06/19 05Z 1.22 2632  97  68   7 0.02
Fri 06/19 06Z 1.19 2632  96  66   7 0.02
Fri 06/19 07Z 1.02 2632  95  66   7 0.01
Fri 06/19 08Z 0.95 2633  92  67   8 0.01
Fri 06/19 09Z 0.91 2634  90  65   9 0.01
Fri 06/19 10Z 0.91 2634  91  59   9 0.01
Fri 06/19 11Z 0.90 2633  92  60   9 0.01
Fri 06/19 12Z 0.92 2633  92  56   9 0.01
Fri 06/19 13Z 0.96 2632  92  61   9 0.01
Fri 06/19 14Z 1.06 2631  92  54   9 0.01
Fri 06/19 15Z 1.13 2629  90  47   9 0.01
Fri 06/19 16Z 1.37 2627  91  42   9 0.00
Fri 06/19 17Z 2.59 2526  92  44   8 0.00

Run total areal avg QPF for the Central_Greens is: 1.39 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